You should purchase a new skateboard if you outgrow, damage, or wear down your current skateboard. When a skateboard is outgrown, a person’s riding stance becomes smaller and feels relatively cramped. Typically, most people don’t have to worry about outgrowing their boards, but younger children and their parents do. If you damage a board--like cracks begin to appear or it begins to fall apart--you need to get a new one.
Damages like this typically cannot be fixed, or the amount of money you’ll pay to fix these issues isn’t worth the effort. Finally, issues like wear and tear are up to each individual. Items like worn-down wheels can be easily replaced, but worn-down decks aren’t so easy to repair. As a general rule of thumb, replace your skateboard once you notice changes to its riding and cruising ability.