I’m doing that now out of necessity.
But I wonder if lowering food intake at my age will also decrease muscle mass.
I have the same concern. Gaining muscle after forty is extremely difficult. The key is not to just reduce the amount of food. More important is the quality of the food and the fat/protein/carb balance.
Exercise however is the deciding factor. Not hours in the gym. Just a 30 to 40 minute walk every day and some light resistance work combined with sufficient animal protein in your diet is all you will need.
At fifty I was a dedicated gym rat; a lean and hard 180. Now in my seventies, I hover around 140; still lean with good muscle definition and I haven't been in a gym in 15 years.
That has been my experience. FWIW