How long should I wait for my PS3 to cool before playing again?
You are free to wait 5 minutes or more depending on the ambient temperature near the console, but for a console that has more than 10 years ill recommend swapping the thermal paste in RSX and CELL-BE chips, and if is one of the Fat models or a Slim 20XX, a change of capacitors so you don't get the Yellow Light of Death in the future.