If you still have a full head of hair at...?

I started college last August and I noticed quite a bit of people who seem to be losing their hair. This got me thinking about my own fate. I've always been told by barbers that I have unmanageable thick hair. So does my paternal grandfather (he's 85 and still has his juvenile hairline). My maternal grandfather is 75 and isn't bald -- his hair is just thinner, probably from old age, but he shows no signs of balding/bald spots. Same thing with my dad, who's in his mid 50s. However, my dad has *slightly thinned* at the crown but I suspect this has to do with his increased stress at work and my college tuition and his mother's illness. His hairline is the same as when he was younger. So my main question is -- since both my dad and my grandpas have hair at their respective ages, will they ever go bald down the line? People always say look to your relatives to predict how you'll turn out, but what if any of them go bald later even though they have hair now? Thanks.