Just turned 18, receded temples and hair is starting to thin? (Pictures Included)

[Hairbrain]

It looks to be thinning. Not to sound like a Jerk but its really really simple look at your father, now look at your maternal grandfather. If either are bald chances are you are going to have some level of hairloss, if both are bald you will be as well. If there are others in your family that have hairloss then yes its definitely MPB.

My father has absolutely no balding, my maternal grandfather passed away with a full head of thick grey hair. I on the other hand started thining at 15 and ended up a NW6 by my early 20's. Yes MPB may be hereditary, but those genes can come from anywhere, and there is no simple determining factor. For example, my father has 5 brothers in his family, two of which show signs of hairloss the other three none at all. Wikipededia under "hairloss" gives basic level of information in how genetics may play play a part in MPB.