bigmuscle.com has always had an age check box. (Just go to their
main entry page and you'll see the check box.) I think this new page that you have referenced is designed for those people who are coming to big muscle from an outside site and are linking to a specific profile. This was the back door entry to bigmuscle and they have tried to close that door for them. Everyone is trying to cover themselves now.
Of course a 12 year old can click a check box and make their way into a free site just as well as a 41 year old.