AC not cooling properly?

This is in an apartment. I called for maintenance and they said everything checked out okay. The temperatures at the vents were around 70�F, but the apartment remains about 80�F all day until the sun is down. It's actually still a bit hot until early morning. Does the age of the AC have anything to do with it's ability to cool? The guy said it was because it was very hot outside, but every other place we've lived at the AC could still cool the place off even in 100�+ temperatures.