How to know true love? ?

I'm sorry, you sound like you really did have strong feelings for her, and I don't think you can put an age limit on these things. If there's really no hope of getting in touch with her you have to try and move on, especially as you're still young and you don't want to look back in a few years and think, I wasted my youth. Maybe don't give up 100% though. Miracles can happen and you sound like you deserve it.