I don't think you have to be a certain age, I know I've bought money orders for several years. I've purchased some at Smiths grocery store (cheaper) but now I only get postal money orders. The reason is that if they get lost when sending them to somebody postal money orders are a lot cheaper to get your money back.....I had a $60 money order from smiths get lost in the mail and it cost me over $12 to get my money back, where the postal ones would just be a couple of dollars I believe.

To get the postal ones just go to your local USPS post office and ask for a money order. You tell them the exact amount you want it for and give them the cash for that amount. They'll print it out (it does cost some for a MO but it's not that much) and you fill out the to/from information. It's better than a check because it doesn't have to clear first (If you are sending a check for payment at a business they will have to make sure the check clears before they will send you the product).