I am 49 year old. I have reduced 6 Kgs and maintaining it for last 2 years nicely. Due to busy shedule I don't get time to exercise regularly. But I walk for half hour daily. My diet includes 0.8 gm/kg body wt proteins. I am little overweight but in good health. Only thing is whenever I go for BCA my muscle never increases. I know there is a decrease in muscle mass due to age. But what other things should I do to increase muscle mass? BCA machine shows my muscle mass- 20.5 - 21.5 % Fat mass- 39 - 40 % Weight - 60 Kg Height - 154 Cm
Strength exercises, tending towards lower reps and higher weight, is (more or less) the only thing that will increase muscle mass, or at least maintain it (within limits).
I'd consider 40% bodyfat past the point of being healthy, IIRC in the US 25-30%+ is considered obese*. If it were me, I'd focus quite a bit more on reducing that, rather than trying (specifically) to increase muscle mass.
On the plus side, bringing up muscle mass will increase resting metabolism, which will help bring the body fat levels down. For me, short circuits of body-mass exercises hit the sweet spots between muscle mass, metabolism, effectiveness, and likelihood I'll actually exercise.
Consider the bodyweight and equipment circuits of pehlwani/kushti (पहलवानी/कुश्ती); I find them incredibly effective (if not a bit painful if I "misplace the mace").
*Noting that there's some debate about what a "healthy" body fat percentage is.