well, I was given a slight bit of bullying in my younger years. Not quite the same age situation, but the concept isn't unheard of. You might have already heard such things, but bullies have differing reasons for what they do. Though most of the time the reasons just simply stem and thrive on insecurity. As well as feeding of the better nature of those they bully. In this case, the person doesn't care if you're bigger or older. If the bully doesn't perceive you as a threat, they assume you aren't gonna fight back or assume you show mercy/pity/lack of action cause of their stature. This can also be applied to a female bully on a male target. Does the male not act on their aggressor cause they were taught to not lay a hand against a woman? Would the person hold back if they were given the chance at a fair fight/debate/confrontation? Sometimes people bully cause they want attention. Sometimes they bully until you lay down your thoughts or terms. Sometimes it's just simply out of boredom. The embarrassment is understandable, but it's ultimately gonna cause problems if you remain quiet on the situation. There might even be a hidden connection or explanation between the friends and the younger bully. Cause there's always a chance that the kid tries to get back at someone through their friends. I might be giving the kid too much credit, but it shouldn't hurt to be honest with as many people as you can. If they don't take what you say seriously, when you mean it, then you might wanna reconsider who your friends are.
Although I sympathize that this is just a recollection on your part and things can't be changed at this point.