I read somewhere that John Adams, the 2nd President of the United States, was not a particularly eager student and when he finished the preparatory school that existed in his time, he didn't want to go on to college. He enjoyed the outdoors--hunting, fishing, etc., not sitting behind a desk. When he told his Father this, he agreed that John did not have to go if he didn't want to, but that if he was not studying he must work on the farm. John agreed to this, no doubt thinking that anything outdoors would be preferable to studying books indoors. As time passed though, he changed his mind and when it was time to register for the next term he was quite ready to enroll in Harvard.
I believe John's Father was a wise man--he didn't argue, cajole, or even force John to go to college, but neither did he throw his hands up and allow his son to become a lazy bum. His actions showed John the two roads ahead of him--he could work with his back or with his brain. He believed his son needed to be busy in something useful, either work or school.
As citizens of the Lord's kingdom, no matter our age, health, or abilities our King expects, even demands that we be busy in His kingdom. To use the analogy of John Adams, you will either study and prepare yourself or you will begin working without such preparation, but you must be busy.
"But I can't preach or teach publicly" you cry. I don't question that, but what CAN you do for the Lord? Your health may not permit you to do as much as you used to in the Lord's service, but is there not something you can do? I tire quickly of those who are continually giving excuses as to why they CANNOT work for the Lord, rather than finding a way around their obstacles to fulfill the Lord's commands. I suspect the Lord does too, especially since He KNOWS whether they're excuses or reasons.