Bed wetting (called nocturnal enuresis in the medical world) is common for kids up to 5 years old. It's a normal part of a child's development and typically stops once children reach the ages 5 to 7.
There are, however, kids who wet their bed until a much older age. This can, of course, cause a huge amount of anxiety, embarrassment, and get in the way of fun social activities, such as sleepovers and school camps.
In the last few years, I've treated many kids, the oldest being 12 years old, for bed wetting. Many parents I met have exhausted traditional options such as bed wetting alarms - to no avail - and do not want to resort to medication or other more extreme treatment options.