Is our age gap weird?

Alright so I’m 16, turning 17 in August. Last year, I stayed at my cousins house (he’s 18) and he brought his friend over (it’s one of his karate students that he developed a bond with) and he stayed with us. I stayed most of the summer with them and we did a lot of fun stuff together like going to Cedar Point several times and going to the mall, but I caught feelings for him.

I thought that he was 15-16 by the way he looked and acts, but it turns out that he’s actually 13 years old, as of December 2017. We’re all very close and we’re all best friends. We’re comfortable with each other and we all still hang out together all the time. His siblings and his parents love me and everything seems to be in place, but is our age gap weird at all?