The age has lowered a lot since when I first joined in. It's very hard to tell. Either way, I don't care. I'm very straightforward with my opinions. Whether young or old. Love it or hate it. My advice is there along with others. I was in your same opposition a year or two ago. Don't worry. You'll be 18 soon enough. No more sugar coating, if that's what bothers you.
I'm assuming you're the user who posted the 40-year old guy and the everyone outside is naked questions? (Get an account, you bum! We can't tell who you are!) I think it could be that people interpreted the questions as someone only someone a little younger would post. I don't want to say childish, because I don't feel that way. I thought some of the responses were gold. I had fun reading those.
But yeah, it could be the content of your posts that make people feel you're in your mid-teens, or alternatively, people don't want to risk talking to someone as is they are 18, when they turn out to be 12 or something. It's weird, man. Nothing personal.
It's quite easy to estimate the age of someone if you judge by the way the write and how mature their opinions are actually. I'm not sure though, I haven't gotten any comments from people who think I am 14 (not yet, atleast).
Because we have no way of knowing for sure and ever since the site lowered the age limit to 13, most users probably feel that they should be careful with what they say just in case it IS a 13 or 14 year old. This is why I think the admins should form a new age group like "under 16" or something since there is a big difference between a 13 year old and a 17 year old.