Although I don’t teach it, I took a primary series Ashtanga class twice a week for a year and a half in my mid-30’s. I’ve done both cued and Mysore-style classes.
The nice thing about an Ashtanga practice is that it’s very predictable. A good instructor will know how to show modifications for the series. The poses are very common yoga poses, just in a specific sequence. If well taught, (underscore on the well taught), there will be a safe option for nearly anyone who attends class.
Mysore style, which is a silent practice and more “traditional” Ashtanga, would be best for an experienced class since there are no verbal (or very few) cues.
I teach a vigorous vinyasa-based class and I have people from their 20’s to 60’s take my class. The key to a good yoga class, in my opinion, is acceptance and non-competitiveness. It’s not about attaining a specific perfect-looking pose, but about how you feel while flowing through the poses, a moving meditation at each person’s own level.