How long between upgrading PSU?

[Broken Hope]

PSU's are supposed to get worse with age due to components becoming weaker as they get older and such, how often do people upgrade their PSU's? I have an Enermax 720W that is over 4 years old, is that too old?

 

[Broken Hope]

Depends very much on the quality of the PSU. New, good quality units don't suffer from the same degradation as older/lower quality units.
Which Enermax do you have? Your system really isn't pushing an overkill unit like that.

I have the infinity 720W, it's a good PSU, never had an issue with it. Though thinking of getting a Corsair one due to the all black cables, flat cables for drives and the fact the fan doesn't spin up until around 50% load.