Is it possible to ascertain if someone who is 18 will go bald in the future?

Not really: Wait a few years. The more chest hair (which most people think looks good on a man) & beard thickness, the more likely the man is to have early hair loss. Look around and you'll see this is true. Some women prefer a hairy, balding man; others prefer a smooth man; most are most concerned about who the man is, his level of fitness, earning power, whether he is affectionate.