As soon as it is (1) possible, and (2) in line with your goals.
(A follow-up to this post about bodyweight-only training.)
#1: How do you know when it’s possible? When you have proper form & range of motion.
If you don’t have proper flexibility, and you’re in my garage, you’re training with a PVC pipe. That’s not a ‘demotion’. Loading a bar on your back when you cannot squat with your butt down to your ankles without any weight, keeping your spine and core straight, with your feet solidly on the ground, is stupid.
Would you ask someone hanging off the edge of a cliff to hold a bowling ball?
Flexibility is the equivalent to your ability to pull yourself back up to safety on your own. Adding the bowling ball is the equivalent to dangerous coaching. Falling off the cliff is the equivalent to getting injured.
You are only as strong as you are flexible. In other words, if you don’t have full range of motion, then, I don’t care if you can squat 500 LBS to 90 degrees. At 91 degrees, something’s going to pop, therefore you cannot really squat 500 LBS to the full range of motion.
Be humble and smart. You’ll end up much stronger in the long run when you achieve full range of motion first.
For #2: Training with heavy weights might not be in line with your goals.
For example you might have an injury, or, you may have already spent many years training with barbells.
Your training age is not the same as your age. I’m almost 40, but I’ve only been training with barbells for about 10 years. So I am relatively young in terms of training age right now. However, as each decade passes, my ratio of bodyweight-to-barbell training with shift.
So, when is barbell training in line with your goals?
When you want to be able to conquer anything. When you want to become a beast. When you want to be as strong as you can possibly be. When you want to break down barriers. When you want to test yourself mentally and physically. When you want to dominate at work. When you want to be able to carry your family on your back. When you want to build confidence. When you want to crush any obstacle that comes your way.
That last part is what I think about when I step into the gym.