I think it really depends upon whom you ask. ;}
It doesn't hurt to give young rabbits grass hay... it can actually helpif you start giving it to them early (in addition to alfalfa), so theydon't go on a "hunger strike" if you suddenly switch them fromall-legume to all-grass.
As for when to stop feeding alfalfa... I've heard everywhere from 6months to a year or more (longer for larger breeds).Personally, I still feed Meat (who's about 8 months old, now) a smallamount of alfalfa (less than a handful a day), in addition to a varietyof grass hays (I believe Meat eats a pile of hay about twice her sizeevery day... and Meat's pretty big ;} ). From whatI've read, feeding limited amounts of legume hay shouldn't be a problemfor at least the first few years of a rabbits life, unless you startseeing signs of bladder sludge or kidney problems.