"Oh, but you're still so young"

I will hit the next person telling me "Oh, but you're so young". Seriously.

Yes, I'm young. Yes, most of my life is still ahead of me. Yes, I do realise that and I am really grateful for it, but don't treat me like I've been born yesterday.

I may be young - and by young I mean younger than you, according to the relative, arbitrary number-of-years-since-you've-been-born criteria, but that doesn't mean than I don't have feelings.
That doesn't mean I haven't grown attached to things and places and people. That doesn't make leaving them behind any easier.
My feelings are real and my mind is just as alive as my body is. Can you say the same thing about yours?

The fact that I'm young doesn't say anything about the things I've lost and the times I've been hurt, it doesn't make the scars on my mind or the deep cuts all over my soul go away.
Sometimes I feel so old... Trapped in a young body with soft skin and a perfect smile, I betray your eyes. What you get is not what you see, but I guess that's what you deserve if you're so eager to judge by appearences and label people you don't know anything about.

You may be older but that alone doesn't give you the right to be condescending - aren't you supposed to be wiser than that?

I'm sick of being looked down upon just because I am "young". It doesn't matter what I do or what I say or how smart I prove myself to be - I've been shoved into the "young" box and that label won't come off my forehead. Don't worry, that won't stop me. One day you'll be left wondering what hit you, calling it luck, ignoring the fact that I've been constantly getting better right in front of you.

You can treat me anyway you want and there's no way I can stop you - you won't see anything other than what you expect to see.

Just don't expect to get my respect by default because you're older.
The people I take seriously aren't categorized into age groups.