Why should anyone perform an exercise that is useless, regardless of age?
Talk about age discrimination. I would counter with the argument that OH squat also improves posture and indoctrinates a good back squat form, because as others have said, you can't do these with bad form. The only difference I see between the setup and movement of a back squat vs OH squat is the positioning of the bar and consequently, the arms.
So, you're giving up on life? I compete in life and I'd like to keep a strong core. I don't know of any movement that incorporates the 'body as a whole' other than the Olympic movements, but the OH squat is a 'safer' lift than those because they aren't as explosive and the weights used must be lower.
Personally, movements that work, work. If they work, they are worth doing. I won't stop doing them because someone else thinks they are worthless.
As for the original poster, you haven't given enough information for us to evaluate where your problem is coming from. It is possible that the OH squat is causing your pain, just like any squat movement can cause knee pain if done improperly or if it aggravated an existing problem. You need to focus on what's going on with your body during the OH squat. Therefore, I echo what another poster said - use a broomstick and empty bar until you've got the movement down pat. This is really the only way to get your shoulder and hip flexibility to a point where you can add some weight.