Given that you have prior boxing experience, I would recommend doing dutch kickboxing rather than muay thai. There is more use of hands in Dutch-style so it will be easier to get used to in your case. Age-wise 35 is not too late. Given that you are fit and have prior fighting experience, you should be able to start sparring in around 2-3 months and start amateur fights in 6-8 months. You can see how you are doing in the amateur fights and if you feel like you are confident and you are winning your matches than you should be able to become a semi-professional. The reason I am saying semi-pro is because 35 is too late to go fully pro and make a living just out of fighting. You probably won't even be able to make much profit with the costs of purchasing equipment and gym membership. So, you will be lucky if you can even make some profit while fighting.
