He’s younger than me

I have this guy that I met about 2 years ago, we’ve become really good friends however in this time I’ve grown to develop feelings for him beyond friendship. The issue I’m having is that I’m not his type , I mean I’ve never asked him but I’m sure he’s not into me. Not only that but he’s 5 years younger than I am , (He’s 21 I’m 26. ) I don’t know what to do , I’m into one of my best friends. We get a long so well and talk to each other about everything! How do I deal with this?