Is it okay for a 18 year old to go out with a 23 year old?

Me and this guy are really close but he’s my brother best friend like brother, and me and the friend got really close, and I told him that I liked him and it might be just a crush but I think I love him, I think he likes me too but it’s the age thing that worries me the most. We haven’t done anything but kissed twice.

He said he will wait for me until I’m 24 or 28 for us to be a couple, to you know (sex that way we are both ready) but I’m just not sure what to do