Fitness is only once piece in the puzzle of wellness. However, it can be a great start to your journey of stellar health and longevity. These are the programs to choose from to do just that!
Bonus - Meathead's Protocol
I do not advocate working out purely for aesthetics, but I am offering this program to show you what helped me to put on ~50lbs in under 6 months. This routine + significant caloric surplus consisting of crappy protein shakes, peanut butter sandwiches and 10 bananas a day. Hey, that was nearly a decade ago, don't judge me!
Once again - proceed at your own risk. I recommend sticking to whole foods and a slight caloric surplus to target muscle growth. Don't obsess over macronutrients and forget calorie counting.