losing the hair at 18. is that a reason to worry?

I'd say you're in for a premature hairloss!

Hey, 100 hairs would be normal, this is not. Dandruff is also a bad sign. During puberty I had lost no hair at all when most boys have a slightly receding hairline. But then it hit me hard when I was 19. I started to lose hair at the same time on my temples and on top of my head. Just like you, 200/day and dandruff. A year later it became really dramatic. I clogged the shower drain everytime with my hairs, I woke up with hair everywhere on my pillow, I lost hair during the whole day. I was bald when I was 24 and a year later the crown of hair which remained had become very low with only 4 cm of hair remaining on the back of my head.