The life cycle of a Transformer is in many ways very different from that of organic species.
Various means of Transformer reproduction have been showcased in a variety of continuities. In general, these are either non-sexual (mechanical) or asexual in nature.
In most cases, the road to Transformer life begins with the purposeful construction of a body by an existing individual or group. In the Generation One cartoon and Marvel comics, these are always shown as being complete, fully mechanically built and functional, though lifeless, robotic bodies.
Beast Wars, along with introducing sparks, introduced the concept of a "protoform": an unfinished, "embryonic" Transformer body. (In Beast Wars, they appeared as mostly smooth, mannequin-like shapes with an outer layer that resembled liquid metal.) These simple "skeletal forms," as they are described in the Dreamwave More than Meets the Eye guide, are kept covered in nutrient gel within stasis pods that nurture and protect their apparently fragile forms. Since their conception, protoforms (like sparks) have become a recurring facet of Transformer technology spread to post-Beast Wars continuities and have been applied "backwards" to new Generation One fiction created following their introduction. It might be speculated that the needs and realities of the wartime situation in the early Generation One material necessitated the skipping of the usual protoform stage.
Protoforms, though functional, seem to be fairly simple, non-sentient, weak, and fragile. References have been made to someone being "weak as a protoform cybertron" and something being "so easy a freshly fissioned protoform could use it." The Marvel comics make reference to a "Mecha-minder" in a fashion that suggests a pram or other baby-related device. It is possible that this is something that monitors a protoform, as it is the only baby-like stage Transformers appear to experience. In Beast Wars II, protoforms stand and move on their own, but in a sort of mindless, zombie-like manner, despite hosting pre-existing sparks.
Regardless, at a certain point, these newly constructed forms are either "switched on", infused with life from an outside source (see Reproduction), or scan an alternate form, and solidify into a finished, mechanical robotic form. Life begins.
From most of what we have seen, the species seems to have very little concept of childhood as humans know it (perhaps explaining why the Autobots are so prone to taking human children into harm's way). Almost invariably, a new Transformer comes into being as a fully formed "adult" (actual maturity varies according to the individual, usually from early adolescence to full maturity as we humans would reckon it), preprogrammed with a complete personality and most of the basic knowledge necessary to survive and socialize in the world. Most continuities have shown newborn Transformers being pretty much immediately thrust into their new lives and combat duties (though this haste may be a result of wartime necessity and not indicative of pre-war society).
Transformers: Cybertron introduced the concept of Primary programming as sort of an elementary school period which newly created Transformers go through to facilitate their introduction into society. This may be the norm of all Transformer adolescence outside of a wartime situation, though that is only speculation.
Parenthood (past the point of creation) or distinct family units in the social sense are very rare in Transformer fiction. There is the brief canonical mention of Wheelie's parents and the families of the Victory Decepticons, suggesting that some TFs in some continuities do form parental/offspring family units, but these have been rare exceptions rather than the rule. The closest and most common generally recognized genetic/familial link is that of brother- or sisterhood, caused (according to the Dreamwave More than Meets the Eye guide) when a single spark splits before entering a protoform. Such siblings generally remain close their entire lives.
The average life span of a Transformer is unknown. In some continuities, they have been shown to spend millions of years without any noticeable alteration or aging. Skydive stated in the Generation 2 comic that outside of warfare, the race was practically immortal.
It should be noted that despite extremely long lives, Transformers have been consistently shown (especially in the G1 cartoon) to have relatively short memories. Frequently, they forget much about their pasts, even seemingly important things, as if those things never were. This might help explain their relative lack of personality change over unfathomably long periods of millions of years.
In the end, however, "Practically immortal" is not the same as "actually immortal"; Transformers DO age. Kup and Ironhide are prominent examples of aged Transformers, as is Alpha Trion. Both he and Kup are shown to look different and "younger" at earlier times in their lives. These changes seem to be signs of advancing age. While they could also be a simple factor of their gaining new or upgraded bodies, the clear intention is that their later forms are more lined, worn and less spry, suggesting aging.
The Overlord, ruler of pre-war Cybertron in the Marvel UK comics, was apparently dying of old age just as Megatron began his rise to power.
In the movie universe, the aging process of transformers is more inconsistent. The most noticeable case is the ancient Decepticon turned Autobot Jetfire, whose physical body bears large resemblance to a cranky old man. In addition, aspects of his body such as weapons and the transformation process were shown to be either malfunctioning by this stage or no longer as efficient. However, The Fallen was portrayed as one of the oldest Transformers in the universe, being one of the original Primes; but he didn't show any signs of aging. Ironhide was also described by many bios as quite old but again seemed just as spry as any of his comrades. It's possible, however, that both The Fallen and Ironhide didn't display aging due to constant maintainace or replacement bodies whereas Jetfire was left to rust with no outside help at all. A lack of a steady source of energon could also be the culprit, as Jetfire explains that "Without it, we'll all perish, oxidize and rust..." Presumably, Ironhide and the Fallen would have been sustained by a ready supply, while Jetfire eventually ran out of power and began to degrade when he was no longer able to refuel.
This is also one of the few instances where the concept of 'rusting' is introduced to Transformers canon.
Though more difficult to kill than most organic lifeforms, a Transformer can die, either through age or catastrophic damage. Of course, "death" is pretty...vaguely defined for Transformers.
The context for the above conversation was after the Autobot Gears had plunged hundreds of feet to the ground and shattered into multiple pieces. Some Transformers have come back from death many times, while others have seemingly died for good after suffering damages from which other characters have recovered.
A more cynical person might posit that the only thing that actually kills Transformers is the whim of the plot, and even that can be negated later by, again, the needs of a story.
On rare occasion, death is shown to be accompanied by a visible darkening and color-desaturating of the Transformer's body, as featured when Optimus Prime died in Transformers: The Movie. But most often, this is not the case.
When a Transformer dies (at least in fiction from the Beast Era and after) his spark returns to the Allspark/Matrix.
In the Generation One cartoon, when the Matrix-bearer died he joined the spirits of previous leaders inside the Matrix of Leadership. There has been some indication that once a spark has joined the Allspark, it is sometimes reincarnated as a new Transformer, who may or may not have faint memories of its prior life.
- See also: Transformer funerary practices