I have been debating this myself. I have a 17 year old gas heater that came with a 12 year warranty. I did replace the T&P valve in 2009 because it started leaking. Other than that, it runs flawlessly. I will probably just leave it be for a few more years. Besides, unless it fails in a launch through the roof fashion, it is in an area that won't cause much damage.
I have checked new codes and know what to look for and how to install it if it does fail. The fed gov't changed insulation codes, I believe in 2014, so the physical size vs capacity is different. I have not looked much into them because I have gas, but there are now heat pump water heaters that might be more efficient. Whether you replace it now or later, do some research now while you are not in a time crunch because the family wants to shower in the morning.