I'm not an eye doctor, but my guess is they will eventually get worse because I'm so young. Surgery, medicine, carrots. The big worry about floaters is that they can be an indication of a detached retina. Since your doctor didn't see any indication, you don't have to worry about that. People who are extremely near-sighted are prone to detached retinas.
People can get floaters at any age.
Sometimes they can occur from violent activity, like playing football. In most cases they go away in time, but the larger the floater, the longer it takes to dissolve into your system. Floaters sure can be a nuisance though, especially when they get in the line of vision. After a while, they float over to the side. There is nothing you can do about them but to accept you have them.