Sometimes they just start leaking with no previous warning signs. Depends on if you want to deal with it when you want to, or just wait, then it's sort of an emergency. If it happens on a weekend or holiday and you want it fixed, it will cost a premium. If you can wait until the following normal workday, and live with the inconvenience, it's not.
Draining the crud out periodically is a good idea. If there are flakes of rust when you do this, it is time.
The anode rod is probably all used up but getting one that old out might be tough, and might break something else in the process. Depending on the water where you live, replacing that periodically may help prolong the WH's life.
The WH sold at HD are made by Rheme, so if you wish to pick up your own, are not a bad choice. A plumber may not cost more if he supplies one, and then you could get the Bradford White.