A cars air filter should be changed at least once per year or every 6,000 to 12,000 miles.
I change my cars air filter every year regardless of miles.
If I drive in more dusty conditions then I change the air filter every 6 months or so.
But as long as you change your cars air filter every year then you should be okay.
If your cars air filter gets dirty then it can cause loss of engine power, increased fuel consumption etc.
If you notice your car is using more fuel or is losing power then it could be the air filter especially if the air filter has not been changed in a year or longer.
The air filter is an easy cheap replacement part and it helps keep your engine running good.