Flexibility comes before strength.
You may have noticed that, so far, through my first three recommended steps to becoming stronger, actually lifting weights has not yet been discussed.
This is by design. If you lift weights before you have proper flexibility, you will not become as strong as possible, and you will probably get hurt.
There is no reason to put weights on a barbell and squat, for example, if you cannot squat to proper depth at body-weight, with good form.
In fact, by definition, all you will be doing there, if you increase the weights enough, will be heading towards injury. One of your ligaments, muscles, tendons, or joints will be asked to bear a load past the point of what it is capable.
In a person with full flexibility and range of motion, this is OK. The rep would be failed, and the max for the day would be established.
In a person with less the full range of motion, something would snap, or tear.
The good news is that proper flexibility can be achieved with proper attention. It won’t take that long, and it will give you the foundation for real, safe, strength training.
You don’t have to ‘just stretch’ for six months. You can exercise too, while your working on your flexibility.
You might need a coach, which is why you can ask your prospective coach-to-be (in Step 2): “How will you assess and improve my mobility? What positions will I be stable in six months from now?”