I've had three water heaters in the last 44 years. When I moved in there was no water softer and I installed one (on my third one now, finally figured them out) though it's efficiency over the years have waxed and waned. The original propane water heater to the house of unknown age, and AO Smith. It lasted for a few years then started gurgling.
Then got a State and it lasted about 20 years. After a year or so I took the anode rod out due to sulfur smell in the hot water.
Replaced that one just because I was also getting new furnace and AC. I took the anode out of it before installing. It's still sailing along just fine. It's another State.
The anode rods are in very tight and good luck removing one with the tank vertical.
The first thing you should do is get rid of the cheap plastic drain valve as they are only about a 1/4" opening.
Edit: My brother replaced their water heated a few years ago. it was only 5 years old and they were on city water. Being the pack rat I was I hauled it home and was going to clean it up to see if it was worth saving.
It had to have over a foot of sediment inside. Even with the drain valve all the way off it was still plugged up.