I'll keep this simple and to the point.
What follows is what I would tell any young man (or lady for that matter) to do with their physical health at the start of their 20s.
Dont question this, just follow it.
You will learn the answers in the process of doing.
1. Spend your first 5 years of training power building.
This means prioritizing building muscle, and building strength.
Lift to either do more reps, or do more weight. When you cannot do more weight, do more reps until you can.
Repeat this over and over.
Learn how to get stronger, learn technique, focus on tried and true compound movements. Transfer this learning curve over to any other skill
2. Don't fall into believing that the wheel has been reinvented with diet.
It has not.
Eat moderate protein, moderate fat, eat carbs, some can eat more than others.
Do not read “diet” books that use the terms “secret, revolutionary, magical, cutting edge” or any other hyperbole in the title.
Learn the basics of nutrition, and then experiment until you find what works best for yourself.
3. Find a good trainer to teach you how to lift if you need help.
A good trainer, or even a more experienced mentor, it will be very obvious that they lift themselves.
Never work with someone with less than 5 years experience, 10 is preferential.
A good teacher can save you YEARS of wasted time, decades even.
Start as soon as you can, do not wait.
Your 20s are the primetime to establish health and vitality for a lifetime.
Take advantage of time now so that you are not catching up for time lost later.
4. Dont waste money on endless supplements.
Whey protein, maybe Vitamin D, maybe ZMA for a better sleep.
Eat veggies and fruits, you won't need a multivitamin.
Eat enough healthy fats, you won't need fish oil.
A cup of black coffee or a caffeine pill is as good as any pre-workout. If you want to use a nootropic-use this one.
Take the money you’d spend on supplements and invest in a Roth IRA.
That $200 is better spent than on the latest pump product or diet pill.
5. Do not get fat. Do not ever ever get fat.
Learn about your specific body type.
Understand your insulin sensitivity to determine how many carbs you can eat and get away without becoming soft.
If you do these 5 things, you will more than likely be very very heathy and live a long time.