How to convince someone they're not too old for you?

I have this great friend who's 22. We haven't known each other more than a couple of weeks, but I really like him, and I'm pretty sure he likes me too. Still, sometimes he starts going on about him being too old to be my friend. I'm 16 by the way. What can I say to make him change his mind? Do you guys think the age difference is too big for anything to happen between us?
How to convince someone they're not too old for you?
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