If you are an adult, you should have no problem with age. The main thing you have to look at is weight. You can stick to the 10:1 ratio. If you want to buy a bowling ball for a kid, then you might have to use a different ratio. The most common rule of thumb is that if the kid is 8 years old, buy him a ball that has a 1:1 ratio (an 8-pound ball on this case). You can slowly increase the weight as he grows older. This is just to give him a feel of bowling and allow him to practice basic bowling techniques.