Join Date: Aug 2009
Location: Portland, Oregon
In Tales of Heresy, Leman Russ's court of manly men are taken in for Space Marine induction. Most of them were at their full maturity, so past 20 I'd assume. Most of them died, I think about 5% survived and it astounded the Emperor. There's no upper limit, I think, but your chances start dropping like crazy after you hit 18 or so.