年上感がないって英語でなんて言うの？

ーIt doesn't feel like he's older than me at all. We get along ever so naturally.
「全然年上の感じがしない。すごく自然にやっていける」
It doesn't feel like he's older than me. で「年上感がない」と表現できます。
to get along で「仲良くやっていく」

ーI don't feel the age difference between us because he's easy to hang out with.
「一緒に過ごしやすくて年の差を感じない」
I don't feel the age difference. で「年の差を感じない」
to hang out with .. で「一緒に過ごす」

ご参考まで！