I have a water heater that is 20 years old. When we turn up the water temp the pressure release value opens and drains water into the overflow pipe. The issue is this then overflows from the top of the pipe onto the floor and is only fixed by turning the water temp down. The water temp setting doesnt even have to be too high for this to happen. Time for a new water heater??
20 years old, it's almost certainly time for a new one unless it's of very unusual construction - like stainless steel.
overflows from the top of the pipe onto the floor
Then the overflow pipe is not correctly routed - it should go DIRECTLY down to the floor. I can see it going sideways in the picture on your other question. It also appears to be reduced in size, which is a code violation, and if it's positioned so that water is held (trapped) in it, that's a code violation.
Many hot water heaters need an expansion tank to avoid over-pressurizing the PRV when heating a slug of cold water when no water is being used. Most PRVs are rather bad about resealing when they have been "exercised" a bit. Both of these may play into your problem.