Starters on cars will usually last over 100,000 miles between needing to replace them.
So that would be around 8 years on average that a starter on a car should last.
I've seen some cheaper starters only last 3 years while I've seen some starters last up to 10 years. It depends on how much you start your car and how good of a starter the starter was to begin with.
You should at least get 7 to 8 years minimum out of a good starter though before needing to replace it.