Its his birthday on the same day as christmas and I want to get him something special, something he can keep and look back and it bring back memories of us

A photo frame of you both together..
I wouldn't go over board as I have a feeling things may change in the future.

I'm baking several different kinds of cookies for mine -- oatmeal chocolate chip, almond crescents, Hershey bar bars, peanut kisses, lemon bars, caramel brownies, bourbon or rum balls (haven't decided which yet), thumbprint cookie with raspberry jam filling, and no-bake fudgies.

If you need recipes, holler.

A framed picture was mentioned, and is a good idea. Something handmade, if you have that ability, can mean a lot. Anything related to an in joke or fond memory works. Something he's mentioned liking/wanting, is always safe.

I would advise against anything too big until a relationship is a few years old, or you're engaged/married

And, and from someone who's known several people with birthdays on/near Christmas, giving separate presents (and not wrapping the birthday present in Christmas paper) will make a big impression. Possibly bigger than the gifts, themselves.

Does he have a favorite sports team or hobby?

I agree with homemade, and I have kept many homemade cards all my 66 years.
My ex husband made the best pop-up cards. He wasn't a good artist, but he put a ton of work into them, and they were cute and sweet and funny and unique.
I have pretty much forgotten what he bought me, but still have those cards.
Although I can remember fondly some things from my teens, they are long gone.
So don't spend money, at least not much.

Memories are the only real thing that lasts though time. Do not put so much stress into this