So, you want a suit of armor, but you don't have a forge and a small fortune in tools? Well, there are dozens and dozens of entrepreneurs who would just love to help you out. Just make what you can, and buy the rest.
Armor making is a cottage industry. Not many people do it, and they often don't have a large inventory. You want a particular helm? No problem. You can have it made, but it will take months and months.
I obviously have not tried all or even most of these armories, so let the buyer beware. I can't guarantee that all the sites are fit for young readers. But, I don't doubt that most of them are hobbyists like you and me, who support their armor habit by making and selling to their friends.