It isn't too late. But, be careful when teaching it to him, it can be very difficult for him to hold his frame properly. So, just start out with very little. Also, when you are riding him do a lot of double up circles at the walk. What you will hopefully get from that is him dropping his neck slightly, him bending, and him being soft in your hands. Also, before you get him into a decent frame just work on flexion and going forward. I'm fairly certain he will not be pleased with having to work in frame because he has to do more work lol.
"You know, for as long as I can remember, I've had memories." ~Colin Mochrie