None; chest hair and body hair are determined by genetics and age and by nothing else. If the adult men in your family have chest hair, then you probably will get some too--though in many men chest hair doesn't grow in, or grow in fully, until their 30s.
sometimes
It varies dramatically. A few men will have a thick mat of chest hair before they are 18; other men are relatively smooth-chested in their teens and 20s and then develop a lot of chest hair in their 30s. Typically, however, you should have a sense for how hairy your chest will be by the age of 25 or so.
Men sometimes lose chest hair
64% of white men do have chest hair, according to a study quoted by Wikipedia.
It varies. Most men who have chest hair will see it grow up to an inch or so--but it is relatively common for chest hair to get even longer, even up to 2 or 3 inches, at least in patches. If your chest hair gets too unwieldy, you can clip it shorter with regular clippers.
Boys typically start getting chest hair during puberty, which generally occurs between the ages of 9 and 14. The timing can vary from person to person, and genetics play a role in determining when this secondary sexual characteristic will develop.
Unfortunately chest hair growth/pattern has to do with genetics and nothing else: there is nothing you can do to get more chest hair to grow, and the only way to reduce chest hair permanently is electrolysis or laser hair removal. Most men don't realize it, but their body hair keeps growing in throughout their 20s; if you are genetically predisposed to have chest hair, it might start growing in when you are 16, 25, or 30. It just depends. Men with light chest hair in their teens and 20s may find in their 30s that their chest hair gets denser or more widespread. The best gauge is to look at your father, brothers, grandfathers, and uncles: if they have chest hair, you probably will too.
No it can not grow your hair.
Different men get chest hair at different times. Many 13- or 16-year-olds will have some, and for a lot of men their chest hair grows in in their 20s, but most men's body hair doesn't finish growing in until they're in their 30s. You could be completely hairless and then suddenly start growing body hair in your 30s. Not all men develop chest hair, however, but most men have at least some.
Like most things to do with puberty it is very variable and indeed some men never do grow any hair on their scrotum. Next time you go to the beach or the swiming baths you might notice that while some men have a thick growth of hair on their chest, some have much less and others have none at all. Of course some men may have shaved their body hair (and some men also shave their pubic hair and scrotal hair) but many men just don't grow any chest hair at all. Every body is different and some guys have much more body hair than others. If you already have pubic hair, and hair by your anus, you might expect to see some hairs growing (even if they are tiny) on your scrotum, if you are going to grow them.
Different women have different tastes; probably about half of women prefer some chest hair on men--and some of them even prefer LOTS of chest hair.