its a mature hairline your dad has good hair for his age, i wouldnt worry, dont be stupid like me and shave it when theres nothing wrong, in the one corner of my hair, i have some hairs from where my hairline USED to be, that are small and thin(miniaturized) but the actual hairline is completly fine, probably the same as you, i know what its like to get a mature hairline early, i got mine at 13/14, and im now 19 and a half, and my hair is exactly the same as it was 5-6 years ago, when it first matured i got a little worried as well, i didnt look into it at all, then i got folliculitis and i got tiny bald spots from it, i got scared and found this site, and ive been here ever since and im paranoid about my hair, i post here alot, people hate me on here cause i dont friggin listen to them, dont become like me, your hair is fine right now, probably should leave here untill you are actually balding, thats IF you go bald. i dont believe the male pattern baldness comes from one side of the family, so just because your maternal grandad was balding, wont mean you will go bald 100%(to everyone who knows how much im obessed about my own maternal grandad, i know ,i know, practice what i preach),
your not balding right now, and you probably wont for a while