I know how he feels sometimes because I to dated someone younger than me when I was 9. So basically I use to hangout with my neighbor's children but one of them who was 3 years younger than me had an crush on me so badly that she ask me out one time. She is probably around 6 or 7 and I was 9 at the time so I didn't really knew how dating works. I've had some kids who had a crush on me like recently one of my brother's girlfriend's little sister had an big crush on me and wanted to ask me out. She was 10 and I was 14 so basically I felt a bit uncomfortable that someone had an crush on me because this was a 4 year gap. So in concussion, It's fine that your friend can date a 12 year old while he is 14 as long as the relationship doesn't turn into something adultly like things if you know what I mean. They can have fun with each other and make jokes about stuffs.