Off topic or useless can probably describe most of sanjx's and op's posts along with most others on yobit and secondstrade and he's now wanting more kids he knows to do the same and that's why something needs to be done about these campaigns. When they realise they can get paid to post crap why not tell your friends or open multiple accounts to do the same every day?
I somewhat get the feeling that the demographic of most shit-posters is young adults who live in countries that have a lowish standard of living.
I don't think very many 15 year olds (or 12 year olds, or whatever year olds) would have very much use for the money they could earn from shit posting on signature deals. I would speculate that most miners that post here would probably have more of a genuine interest in Bitcoin, and would have some level of technical expertise.
Signature campaign don't really pays you money for shitty posts unless you are in a bot operated signature campaign, that would be possible. Manually ones are much better when detecting spams. I've turned 15 a month ago and I feel that what I can earn from signature campaign is quite useful. I don't post solely for the money but it is more for gaining knowledge about Bitcoin. The money from signature campaign is a huge plus and can help to fund my VPS that I use for hosting and sometimes, I can even spend it in real life.
Anyway, OP, don't worry about age issue, I registered here when I was 13 and I didn't meet any issue. The only issue is if you use a gambling site as many of the locations in the world do not allow minors to gamble.