I'm looking for some advice / opinions on a PSU.

I'm upgrading my sister's computer this week and I'm torn on using her current 600w Enermax PSU which is like 5yrs old or so, or using the new Corsair 650w PSU she bought for the build.

I know the Enermax can handle the load of the new system I'll be building, but my concern with it is just the age of the PSU. Should I just use the new Corsair PSU and not worry about anything, or continue to use the 5yr old Enermax PSU to save my sister money but have the reliability of the PSU looming in the back of my head due to its age? As of now, the PSU hasn't shown any signs of reliability issues.