This question was something I already asked in the Sparity group a while back, but I’ll ask it here anyway:

How many Sparity stories are there where Spike’s an adult?

In this case, a big, tall, and muscular dragon who could do things like wrap a large wing over his beloved and cuddle her closer to his side. Maybe even curl his tail around here or carry her in bridal style fashion with very huge and muscular arms.

7505975
I agreed at least wait until he grows up

These come to mind:
https://www.fimfiction.net/story/17706/the-heart-of-a-dragon
https://www.fimfiction.net/story/2851/like-fine-wine
https://www.fimfiction.net/story/32078/purely-scientific-interest
I'm sure I could name at least a few more, but these are the first that I think about that are also pretty good.

7505975
I mean, that's canon, isn't it? He was an adult at the end of season nine. Kinda bulky for my taste though, and his face is kinda weird. Don't know why they couldn't go the anime route with his design.

7505996
Personally, I don’t consider the future events of “The Last Problem” canon despite being featured in the episode.

7506001
Seems like everyone hated the ending.

7505975
"Adult" is relative here, Dragons live so long that their "naps" last a hundred years! An "adult" dragon would probably be far too big to cuddle with Rarity. Seeing as Spike's a "baby" now, what you're describing would probably be a "child" dragon.

7505982

"I agreed at least wait until he grows up"

Rarity's going to be waiting a long time!

Edit: Here's Rarity with an "adult" dragon: