"You get what everyone gets. You get a lifetime."
In the case of the commercial egg layers from the big breeders, that usually means you received a relatively small body weight bird which reaches sexual maturity early (16-18 weeks avg to start of lay) which regularly produces a large number of eggs (5+/wk, 280-320 yr, seasonally varied) which are quite large relative to body size. Oh, and with good feed efficiency - not into mass on the bird, but rather mass in the near daily eggs.
That's hard on a critter. Very hard on a critter.
and as
@Ridgerunner so thoroughly answered above (Informative post!), the initial stock has been selected to pump out more chicks, no efforts have been made to ensure longevity.
While individual birds vary, and all the trade names out there make it a game of speculations to identify parent stock, the typical expectation is a relatively small bird of relatively short lifespan, whose egg laying generally falls off pretty fast in year 2 or 3. Since they are used commercially for egg laying, and then become dog food (or similar) when productivity drops, and are easily replaced, that constellation of traits suits business needs quite nicely.
If those also suit your needs, its a good choice of bird. If it doesn't - or traits other than egg laying are more important (say, this is intended as a family pet...), look elsewhere.