My wife is experiencing back, knee and hip problems and went from my height to significantly shorter rather abruptly. Make sure you don't have an underlying issue developing.

Assuming you don't, then this is suggesting the need for lower gearing and/or standing up on the pedals. A consistent 9 or 10% grade is a hard climb, especially if it goes on for a few miles, and for me at least, requires frequent changes in position (standing up vs sitting, forward vs aft, hammering vs spinning, etc).

How low is your lowest gear?

Is your saddle possibly higher (or lower) than optimal?

I'm 57, and it has gotten a little bit harder each year for the last 4 or 5.