Why do I feel like I am missing out on life?

I've missed my childhood, missed my teenage years. I've been in 2 serious relationships starting when I was 18 and I'm now 22. I feel so old. I feel like I missed out on everything. I feel like if I break up I am too old to start a new relationship and find a good partner and future husband for myself because I'm afraid of being single, but also afraid of being with the wrong person just because I didn't allow myself time to find him properly.

Why do I feel old? On one hand, I have my whole life ahead of me, but on the other I feel like I've missed everything.