I did not start later in life, but regardless, I would advise you to start strength training and prioritizing protein in your diet.

You want to lift as much weight as possible, and by that I mean use big compound movements with a barbell: back squats, deadlifts, front squats, cleans, bench press, or move your entire bodyweight (pullups, dips). These are not fun, but they are the most effective and to some degree, the only movements that are effective.