Does anyone know if the non custodial parent have to pay college expenses past 4 years?

Very rarely... and then only if it was specifically spelled out as part of a divorce settlement. Otherwise assume not. At that point the child is 21 and able to bear their own expenses as they should.

Most places at 18 it becomes their problem.

What Smoothy said. And the NCP would normally pay child support, not college expenses as such, anyway.