Want to get into Muay Thai

I’m planning to start Muay Thai training in around 4 weeks and since I’m not really in a good shape (only did gym weight lifting and some casual running but running not consistently for the past years), I want to prepare my body since I feel overall kinda stiff and my stamina is wracked.

Is there anything I can do like specific stretching exercises or cardio so I will have a bit of an easier start for training?

Dunno if relevant but 31M, 183cm, 91kg

Also, can you give me some insights of how Muay Thai changed your life or mentality? Or even physically – especially if you started at 30+?

Thanks!