Teen Hair Loss

[John12345]

Okay recently I started noticing my hairloss. I'm 18, my dad is 50 and bald (started losing hair at 30) both his dad and my mums dad have full heads of hair.
I have two questions that have been bothering me: is it normal to lose short hairs more than long ones, as in no longer than a cm or so?
Also is it normal for some hairs that fall out to be thick, and others to be thin?
Do either of these mean I have started hair loss?
Thank you