I wouldn't think that it is ever too late, but I imagine that the transition is very difficult for most people.
Not only is the one-hander very different in so many ways from the two-hander on a technical level. For the sake of your arm, you gotta make sure you're pushing yourself to learn the one-hander (and any technique for that matter) properly enough to make sure that you won't just create another source of injury.
It is easy for people to get very sloppy on one-handers when learning them. In some ways, it's natural to start out sloppy because you might not have that particular coordination (though if you've been playing tennis long enough, I figure this is far less a concern than for people just learning tennis).
You want to make sure that contact zone is in a good place (more in front of your body), but you also don't want to be doing a weird lazy-arm gimpy backhand (doing almost nothing with your arm while your body rotates so that your racquet is just kinda flailing passively at the ball--you don't want to do this).
Another point of difficulty is how you react when you read the ball. While I believe that all good groundstrokes demand that a person prepares far ahead of the ball, it's a very critical point on the one-hander--not because of a notion that the one-hander is the only stroke that needs early preparation (it isn't), but the one-hander has a critically lower margin for error if you're just getting to the ball when you hit that one-hander.
Anyways... I could go on and on... I'll try to drop some tips if you do make the transition.... but just remember that I'm just another student of the game (and I have no certifiable credentials, just my word):
-Practice hitting the ball LOW TO HIGH with the one-hander. Not straight across. You want to develop a feel for a low to high swing. Even when you eventually get into situations where you have to hit almost across the body, the feel of the racquet going even just a bit low to high is important. But practice that low to high motion as you hit the ball. It's more important than it sounds. Yes, nowadays I start my racquet up high on a one-hander, but it dips down and then goes from low to high as it hits the ball. Many people try to flail straight across and the result is an ugly backhand that doesn't do its job adequately.
-THE ONE HANDER DOES NOT NEED A FULL ROTATION OF THE TORSO, in fact.... practice hitting the one-hander with your SHOULDERS PERPENDICULAR TO THE NET before and after you hit the ball. You don't have to be super strict, but at least while learning the one-hander, try not to let yourself open up so much on it. An alternative is that you can let yourself show a reasonable amount of your back to the net, but just rotate enough through the stroke that at the time of contact and all throughout the follow-through, your shoulders are perpindicular to the net. So yes, rotation plays a role and you get power from this, but it's not from opening your whole chest to the net (though some players do indeed finish like that and hit good one-handers, but for now don't sweat that). Opening of the body can be added later, but I think the foundation of the one-hander is in applying your body without necessarily flailing it open. Another way to think of this: JUST KEEP FOCUS ON THE CONTACT ZONE BEFORE AND AFTER YOU HIT--I think the two kinda help each other. As you stay focused, your body usually won't go beyond reasonable bounds.
-Like I said above, KEEP FOCUS ON THE CONTACT ZONE. Before the ball gets to you, you should focus on where you will hit that ball. Around the time you are hitting the ball, you should be focusing on that spot. After you hit the ball, you should still be focusing on that spot.
-HAVE FAITH. If you're gonna commit to learning a one-hander, don't give up on it easily. It's a hard shot to learn, but once most of the factors fall into place, it'll feel like a much easier shot in general (though timing can still be very tough depending on opponents). Know that the one-hander is going to be a tough shot to time, have little margin for error, and yet it's a shot that works at its best when you have faith in it (at least that's how it feels for me--that type of faith is the same that drives me to keep my head down as I hit the ball--because I know the outcome will almost always be good and that maintains form).
Anyways, if you go with the one-hander, good luck.
-Chanchai
PS A picture that I feel helps in understanding the one-hander (it won't tell you everything though) is a picture I saw of Federer's one-hander follow-through. You see that he has clearly hit the shot well, is practically at the end of his follow through, but his eyes are still locked onto the area where his racquet struck the ball. I can't go digging for it right now because I have some stuff to get back to (programming assignment--after typing up this post, I definitely need to get back to it now), but if I remember and find time, I'll go digging for that pic and post it here.