How could my much younger brother's friends be stronger than me?

They probably know certain moves that you don’t (or if you do you might not know how to execute them, or/and you don’t know how to defend those/their moves).
Plus, since it’s a few years ago, that you asked it again, they are more experienced now (than you).

It’s called technique!!! My husband was 6’5” & weighed about 225 pounds. We had a roommate who was 5’4” & probably 130 pounds soaking wet. For some reason, my husband loved to pick on that child. One night he got mad & told my husband to STOP. Hubby laughed at him & continued teasing him. This time he demanded that hubby STOP or he was going to embarrass him. Hubby laughed & thumped him on the top of the head. Before he knew what had happened, the kid had flipped hubby over his shoulders, spun him in circles about 5 maybe 6 times, tossed him on the floor, laughed, & said “do it again & I’ll do worse.” Hubby was furious. Much like you, he couldn’t figure out how that little pipsqueak took him down like that!!! Needless to say, that was the LAST time he teased our roommate. I found out later that the roommate has been a wrestling champion during high school while hubby was partying.

Weren’t your brother & his friend 12 when you asked this 2 years ago??? At 14 they should be pretty muscular by now & you should be too old to be wrestling with them!!! Throw in the towel & let them be the top dogs for a change!!!

Maybe you should try taking a judo class . . .

It’s nothing with you, males are 2–3x stronger by weight than females are. Even at that young age. I’m assuming with a name like @Flowermother that you’re female. You can beat them with technique though.

Age is not necessarily a factor.