I've never heard of anyone switching a suit wardrobe after every few years.
If you do it right, you'll end up with 3-4 classic suits that will last you YEARS. But if you're getting those "trendy" suits then yeah, I can see why people would change their wardrobe every few years.
Most people hardly ever have to wear a suit, unless you're the type that wears one everyday to work. Usually, people where suits to weddings, special events and sometimes court dates
My advice: Just buy a GOOD QUALITY well tailored classic suit (eg. Navy, Charcoal, Grey, Navy pinstripe) with a notch lapel and don't gain too much weight. That should hold you over through your lifetime.