A coolant system in a vehicle needs flushed after every 30,000 miles or every 5 years whichever comes first.
I flush my coolant system out by doing a coolant system flush and changing out the engine coolant every 5 years and by then I have a little more than 30,000 miles on a few of my vehicles.
As long as you're changing the coolant and flushing the coolant system every 5 years you should be fine.