It's one thing to be physically fit. It's an entirely different kettle of fish to be flexible, fast and with quick reflexes. That's why boxers and tennis players are mostly washed up in their thirties.
As other posters have noted, learning how to breakfall is an essential first step in martial arts. It is tough enough for guys in their twenties.
As a first step, I would suggest using the internet to check your reaction time to a visual stimulus. If it is slower than 0.25 seconds, forget it.
Bear in mind any injury incurred may be quite expensive to fix in Thailand.