I've compiled a list of the ages for the races I expect people to be RPing, if this thread turns out well, please request that it be stickied, all material is taken from wowwiki's page on lifespans
Adulthood Middle age Old Venerable Maximum lifespan
Alliance
Human 15 35 53 80 85-130
Dwarf 40 125 188 250 252-450
Gnome 40 100 150 200 203-500
NElf* 300 500 650 700 705-1200(Some have lived 2000 years)
Draenei* See special notes at the bottom
Worgen The worgen curse doesn't affect aging or lifespan, see humans above
Horde
Orc 20 (sometimes 18) 40 65 80 82-100 (Sometimes less than that)
Undead* See special notes at the bottom
Troll 17 30 47 69 70-79
Tauren 15 75 95 110 114-150
BElves 110(or 60) 175 263 350 354-390(Sometimes 2000+)
Goblins* 20 40 73 85 75-93
Misc.
Half elves* 20 62 93 125 128-185 (or 200-300)
Pandaren* 80 175 263 350 N/A
Dragons, etherials, demons, ancients, keepers of the grove and dyrads are all immortals
Special notes, where races that are a bit hard to follow are
Night elves: This is a tricky one to figure out, it can be assumed that a night elf stops aging at 300 years old until 7 years ago when they lost their immortality, so you can have a night elf who's walked azeroth for 7000 years but only be 300 or so on the race chart, adding in the seven years since hyjal
Draenei: Draenei are nearly perfect immortals, no draenei's ever been recorded of having died of old age, draenei who survived the massacre at argus may be as old as 25,000 years, draenei can still be slain with sword and spell, however
Undead: Forsaken are immortals from the moment they're revived, they'll exist forever, not aging past the age they died at plus the years they spent dead before they were brought back
Goblins: Only trade princes have been reported of having died of old age, most goblins blow themselves up in haywire experiments before they hit 50
Half-elves: Some reports exist that half elves share in their parents' extended lifespan, but it varies from half elf to half elf
Pandaran: Due to their naturally secretive nature, no reports of the maximum lifespan of pandaran have been written
Edit: Tacked on the notes