I want to add to Joanne’s excellent suggestions.
Be aware that as soon as you are labeling a class 50+, you are likely to attract a group of people who are not very fit and may be novice exercisers. 50+ is often a definition of ‘older adult’. I myself, even though I am 56, would probably not attend such a class because it is not the view I have of myself.
The challenge with classes is that you do not have control over who shows up, and individual assessments are not possible.
Starting with exercises to improve range of motion and flexibility are a good start, also balance as long as it can be done safely.