Interested to get started but have some questions

I have ZERO experience with this so please forgive my ignorance. Muay Thai(MT) looks very appealing to me so I was thinking about talking to MT practitioners. I have the following questions:

1. I see that the fighting and conditioning work is intense. People seem to be running miles while practicing MT the same day. Can the older crowd recover from this? Can someone start after they are 30+,40+ etc?

2. I am currently treating my plantar fasciitis and AC joint injuries. Is there anything I can do to prepare myself to join a MT gym when these problems are handled?

3. How often does someone train? Assume they are not looking to become competitive fighters.

4. Are there dietary guidelines that helps with rest/recovery?

I used to do weight lifting before and thoroughly enjoyed it. I am trying to get fit again and do something that will gradually make me fitter. I would love your input/opinion on this 🙂