How do I know when my water heater should be replaced?
Your other question implies that it's gas. Yes, there are more efficent gas units (as well as more efficient electric heat-pump units) available now. (Electric resistance units are really about the same since they started using a reasonable amount of insulation on them.)

Waiting for the one you have to fail may mean water damage and replacing it in a hurry, which can negatively impact your ability to shop around and get exactly what you want. You are certainly past the usual "lifetime" of a water heater already, though that can vary with water quality/chemistry.

In some areas significant rebates are available on heat pump water heaters, which are otherwise expensive, but which can (compare YOUR local rates for each) actually be cheaper than gas to run, especially if the "moderate A/C effect" is beneficial in your climate.