User blog comment:NecrusIV/Average age of a Space Marine/@comment-4608429-20120815184347

Dante is known to have lived for 1,100 years, but is almost certianly older. The Blood Angels are alot longer lived than most Space Marines, though, so that's a Blood Angel Specific age. And, if the Sanguinor is Azkaellon, the last of the Sanguinary Guard after the Hearsy, then they could live forever.

Pedro Kantor has lived for 350 years, 100 years of which as a Chapter Master. This would apear to be the oldest a Space Marine can get to while in active service, as Ortan Cassius, the oldest non-Deradnought member of the Ultramarines, is 400 years old, and te codex says that "his arm remains strong", suggesting that at that age most Space Marines are to old to fight on the battle feild.

If I was to put an age on them, I'd say that Scouts are 10-20, Tactical/Assualt/Devistator Marines are 20-100, Sargents are 50-100, vetrens are 100-200, and captians can be anywere between 150-300.