For most boys, what is the average age that they start to grow their first bits of chest hair?

It is individual: Usually for boys, there will be the beginning of hair growth in the immediate pre-pubertal years of 11-12. Pubic hair will become obvious, then arm pit hair and then facial hair. Chest hair in my opinion is usually later. Depending on genetic make up, you may have a lot or a little in these areas. Chest hair is very independent. Some men essentailly never have chest hair.

Late teens: First answer is good. In my experience most men who develop chest hair do so by their late teens and early twenties. It is important to look at the men in your family...If they grew chest hair you probably will too. If they did not....You probably won't either.