My son is 7 and he has been bowling in a youth league for about 6 months now (this is his 2nd session).  He is averaging 82 and uses an 8# Maxim (no reason to worry about the hook yet, we're just working on the basics!).  He is still in a bumper league as, again, he has only been doing this for a few months now.  I wanted him to work on fundamentals and not get discouraged by throwing it in the gutter all the time (the first game he threw without bumpers, he threw a 22...he was pissed!).  He has almost gotten to the point where he hits his mark and doesn't even need the bumpers anymore.  My daughter is 5 and bowls strictly for fun.  She is VERY tiny (she weighs 31 lbs.) and uses the 2 handed chuck method (although, she is averaging 75 by doing it!)!  She does use an 8# Maxim as well (she wanted to be like her brother!).  I didn't want to waste the money and buy her a 6# ball only to have to buy her an 8# later, so, I just taught her to throw an 8# house ball before buying her ball.  The good thing that this has done has reminded me that I used to be a decent youth bowler and I have started bowling again!  Now, if I could only get my average over 200!