well it depends on how hairy they really are. if u feel it looks out of hand then go for it, but if u think it could wait, then dont let what ur 'friends' say get to u! i honestly hate it when women criticise each other over stupid things.
if it helps, i was about 12-13 when i started. i started off with the middle, then a year or 2 later i began to clean around them more, then shaping and yeah ur 'style' of brow that u like just keeps changing=]
I think I started plucking mine at 15? I think you start can plucking them whenever you want, it's just hair. It'll grow back eventually anyway. Just don't pluck too much in one go, try to only pluck one strand at a time. Maybe find some reference pictures of eyebrows you like and then try to match the way they look. That way you probably won't end up plucking too much.