I'm not sure where the 20-25 year figure comes from. That is not supported in the medical literature. A mechanical valve should be expected to last a person the rest of their life.
Have a read of this 30 year study on the St Jude mechanical valve. 30 year freedom from reoperation was 92%.
My surgeon and cardio said that my mechanical valve should last longer than me. After I got my St. Jude implanted I looked up my valve model on the FDA website and there was only 1 failure of my model recorded.
