Watch out karting can be addictive! I am 64 yrs old and started karting when I was 12. Last year I switched back to sprint karting after many years road racing karts. I race in the TaG Masters class which is the class I would recommend for you. I live in Atlanta, but race mostly in FL in the FKCS series. We raced a few weeks ago in Monticello, this weekend in Orlando and the next race is the May 18 weekend in Homestead.
A new kart is a better bet, but you can find very good used karts, but it is buyer beware, therefore for someone new like yourself it is best to go to one of the big kart shops in FL that service the FL tracks. I work for and buy from TS Racing in Bushnell, but there are several others that will discuss with you the pros and cons of new vs used.
Lot to think about and tough decisions to make, but soon you will be on the track having a blast! Send me a PM if you have additional questions and I will try to help. Jim