If you want to buy a bike when you're 16 and you wait until you're 15 to start saving, you will have to put away about $335 per month to cover the average cost of a bike — about $4,000.

However, if you start saving in a savings account when you are 12, because of the interest you'll earn, and the amount of time you have to save, you will only need to put away $80 per month.

If you saved $60 per month (or just $2 a day) from age 12, when you reached age 20 you would have $5,760. If you put that money into an interest-paying bank account you would have earned $6,315.

That's $555 in extra money that you would receive just by keeping your cash in the bank!