Can MPB start at 15 years old?

Yes it can start at 15.

Started earlier for me, pretty much right at puberty. I started noticing it when I was in 7th grade if I remember correctly.

Damn dude. This is why I don't come in here crying even though my hair looks like shit. I started balding at 22-23 and I thought life sucked, but losing hair at 13 would have been much worse. Greatjob you are a warrior.

Yes it definitely can. At 16, when people started noticing my hair loss, I imagine I had already lost 50% of my hair. I remember as far back as 13 years old shedding a large amount of hair in class when I rub my head. At 14 my hairline "matured" and took on this asymmetrical shape,as opposed to a straight line. I thought nothing of it, and didn't even care because I had "so much" hair, little did I know that was the start of my MPB. But yeah 16 was when it was noticeable, so 15 year olds are not safe from MPB.

Looking back at my hair loss history and when it started, I can't believe i'm at 24 with only a diffused NW3. It's not where I want to be, but damn, it could have been a LOT worse were it not for finasteride and minoxidil. I could have been full blown bald NW9 at the pace it was going pre-drugs.

Mine was also in 7th grade.

I had a big shed at 16. Though my hairline definitely thinned out it wasn't that bad all things considering. My hair remained the same until I was about 19, where I began shedding again. It does happen that young, I was fortunate enough to not have any further loss between 16 and 19 but there are some people who go past NW3 even before they finish high school (though it is rare).