I learned from a YouTube video with David Swenson, that P. Jois was 60 years old when he had 3 students. And he kept teaching and teaching not gazing at any result. A world movement developed.
For me this is encouraging. Too often we use age as an excuse not to do anything. It's too late, we think. There is a limit to everything and this is the death. Till then let us keep doing what we love to do.