What Kit said. I'll be 50 next month and it is getting harder to do standup. I have my good nights and my bad nights. I find I love groundwork more and more, not because it's better or such, but because it's easier on my body, and yes in my younger days I did lots of groundwork as well as tachiwaza.

For most of the classes I teach, I will warmup the class with groundwork before we go onto standing practice.

Peace

Dennis