(If it's a chocolate pie - Lenalee? XD) Presumably, if Suman ate that much, people wouldn't be shocked at Allen - besides, he would've been in the Order for three months when Allen was too, right? And he's probably not the first to have one (Cloud's monkey, for instance). You may have a point about the teenagers thing, although Lenalee is probably past the rate of growth... and Allen could just be a pig. =P I mean, yeah, he eats a lot due to his Innocence, but it also seems like he really enjoys it.
First off, Kroy is also very new to his innocence, and it does feed off of Akuma when activated so that might help. Secondly, we have no idea how much Suman ate. Thirdly, we have two mid-teenagers. I wonder who would win the pie eating contest?