That's part of what I truly enjoy about this. If you get a boner, wonderful; if you don't, it's not a big deal. Quite the reversal of the typical naked yoga classes wherein the FAQs always make some sort of statement like, "if you get a boner, it's no big deal.""
But, the other thing that makes it possible for older men to participate is that not all poses are strenuous.
Or require you wrap yourself up like a pretzel
Many poses are easy to achieve
Additionally, you should always tell your Yogi before class begins of any physical limitations or medical conditions you have. My instructor knows of my M.D., and he keeps a very close watch over me during classes.
I know several of you readers out there do yoga, and practice Tantra.
Let Stan hear about your experience(s).