Everyone Should Be Stronger Than They Are Right Now
I'd say that pretty much everyone on the planet would benefit from being stronger. Whether your 12 years old or 84, you'll benefit from some form of resistance training.
I know it's a bold statement, but here's why....
'Strong' is a term that leads most people to think 'muscular' or 'big'. The reality is, a lot of people are strong, but don't necessarily look like they have a lot of muscle or strength. Strength is bigger than just having more muscle, it's the ability to have generate or resist force using the contractile elements in your muscles.
Let's think of a rubber band, it stretches as you pull it apart (apply force) and then it returns back it's shape as you let it. The ability for the rubber band to resist force (technically apply force back to you) is detrimental to whether or not the band will snap or not. If you pull hard enough, you'll eventually snap the band. If we look on a bigger scale, say, a steel cable. It might not look like it flexes, but under enough weight it will stretch to a degree. In the same way a rubber band can undergo a certain amount of force before it snaps, a steel cable can likely undergo more because of it's ability to resist or overcome force that is being applied to it.
Now let's move back to your muscles. Everyday your muscles & joints undergo different loads & forces. Hopping in an out of the car is going to load your hips, legs, back, core etc. Cutting some vegetables is going to put force through your shoulders, wrists, arms. Sometimes the forces are small, other times they might be more. A lot of people hurt themselves performing simple daily tasks. All it takes is one time bending a certain way, and your back muscles are unable to resist that specific level of force, and boom, you feel it strain. This is why we prioritise both strength & movement.
At the end of the day, being stronger allows us to be more prepared for the stresses we experience in life, both planned & unplanned. Coupling this with movement (flexibility) we build a body that is adaptable and resilient and less prone to injury!
For most people, it's just about getting started, and then going from there!