[AdmiralSavvy]

POTCO is, like Miss Hexsilver said, very kid friendly but can be enjoyed by everyone. So it doesn't matter if you're young or old, if you enjoy the game, then you're fine. =)
In my opinion, you'll never truly know if they are more adults than kids or vice versa, (although I think that there are more adults). Why do I think this? Simple, kids can act like adults and adults can act like kids, and I speak from experience when I say that there are both...

You'll never know the person behind the pirate unless you make that happen, (which I highly doubt anybody in their right mind would allow...), so you never really know if there's something wrong with the person's thinking and what not. Someone who acts 13 can really be 31 for all you know. In my HONEST opinion, age should not be a factor of consideration while playing the game, it's against the rules, and plus, it doesn't even matter.
For example, if somebody acts immature, you can assume that they're a kid, but you'll probably never truly know.

The bottom line is that these are cartoons, played by real people that you've probably never met. Age is only a number, and believe me, there are plenty of people from every age group playing this game. You're not the only one.
Quitting Pirates is entirely up to you, but I wouldn't recommend it. Like I said, if you enjoy playing the game, you're just fine. People who seem to treat you differently because of age should just be ignored.