Should I learn TKD. I was 18 when I learned KM. I'm now 52. ?

Like the last poster said, age shouldn't discourage you, particularly if you are still practicing gymnastics as mobility probably isn't an issue for you. One thing I could caution you against is comparing your KM experience to TKD. I took TKD for a some time and then tried a KM class and traditional Kung Fu and it was like learning how to walk again. The movements and pacing are completely different from style to style but if you go at it with the right attitude you will have a great time and learn something that is truly worth the effort. Good Luck!!