is 47 too old

To start learning martial arts?

nah

If your interested in learning martial arts, but don't want to be around little kids, you can take private lessons.

Thanks. I found a local school that teaches seperate women's self-defence. I think i might try it, if it isn't too expensive.

Midlife Crisis!

Been there, done that.

At 59 I feel more content with my life now than I have ever done before.

Default data drive has diminished and it seems that as a consequence of this the importance of socio-conceptual aspirations and assumed obligations has also diminished.

In short; I tend not to worry much these days.

Stuff that once seemed so important, no longer does.

Possibly. 

Depends on what you are going to do with the martial arts. 

Destroy my enemies.

How old are they and how long have they been doing martial arts or something like that for? 

LOL, yeah midlife crisis, just accept old age

The best way to destroy enemies is to ignore them.

It's too late to master one, it's not too late to learn one to a medium level.

It depends on what you are trying to learn. It takes 5 to 10 years to truly master an art. Some people are just naturals and can do it faster, but that's the timeline if you have to learn it from the ground up (at least that i've noticed). I've done other martial arts like Karate, or taekwondo... and those take time to master. They are more like gymnastics in the sense that you have to learn movements and other challenges that are more "showy" ... But ultimately from all my experience, I would recommend either kickboxing (muay thai) or jujitsu.

Jujitsu is more a one on one fighting style, Muay Thai you can mess a lot of people up. For 47, i would recommend kickboxing. You would be past your prime, but you can still learn to mess people up with Muay Thai / kickboxing. That sport utilizes the most devastating punches and kicks. It's basically what you need to know. There is no showy stuff, there is no "art" really... it's just... this punch knocks a person out once you got it, this kick will blow a person's knee out... learn it. 

These two martial arts i think you can learn at any age. Jujitsu is a lot more complicated so if you want an ongoing challenge go with that... but, if you just want a damn good workout at the same time as learning things that would mess people up... i would go with kickboxing / Muay Thai. I'm more a stand up fighter so i have that bias. I just don't like rolling on the ground with others... since i'm not trying to be pro... i don't want to get skin infections from doing that... bc you may. I'd rather i have the most knock out power in my kicks and punches. But, it's good to at least try wrestling or Jujitsu to know how to get back on your feet... there are gyms that teach both. Knowing the fundamentals of ground game will help you stay on your feet.