All extremist diets are complete and utter bullshit. Keto, carnivore, vegan, paleo, all silly shit.
Figure out your basal metabolic rate. Start there man. Then either add or subtract calories from that number based on whether you want to gain or lose weight respectively.
Don't eat processed or refined sugars.
Avoid trans fats. Moderate your saturated fat intake.
Make sure you're taking in a decent amount of complex carbs rather than simple, as they're high in fiber.
Eat tons of veggies and a good amount of fruits.
Lean protein is your friend, whether you're training or not, that's a fact. My staples are ultra filtered milk, eggs, fish, and steak.
Train. Don't just move for the sake of moving, but train. Training is exercising for more than just exercise's sake, it's exercising with a purpose and a progressive goal in mind, whether that be strength, speed, endurance, power, flexibility, or sport specific performance. Training will aid you to keep from getting too burnt out and it will help keep you motivated to keep moving and exercising throughout the years, whereas moving for the sake of moving just tends to get old after a while for most folks. Make your movement meaningful towards an end goal, and it will matter more to you.