I was always interested in practicing a martial art, and was torn between Karaté, Judo, BJJ and Taekwondoo. My goal is not to compete but to get committed in a self defense community and get/maintain mobility, strength and logetivity. I am 1m90 and weighs around 78kgs (so relatively ectomorph). In my whole life I mostly ran 8km to 16km with a couple of semi marathons, and done few occasional Karaté, Aikido and Taekwondo trainings (no serious commitment). My heart says Judo is my thing but reading in the forums, BJJ is gaining some interest in me.
My two cents: first of all, self defense is a fairly specific topic, and you will likely not learn the thing I would consider to be the most essential in self defense (situational awareness) in any of the disciplines you mentioned. Judo and Taekwondo these days tend to mostly (if not completely) neglect the self-defense aspect in training, so please bear that in mind. With Karate, it will depend mostly on the school, but in general, that's not the direction I would first point you to in that regard either. With BJJ, it will also depend: while self defense is adressed specifically in some schools, in others it isn't. You will likely not learn good striking in BJJ, good takedowns are also a rarity there (at least from my point of view - my background being freestyle and Greco wrestling as well as Sambo with a bit of cross-training in Judo on the side; I have coached some BJJ players up to black belt in takedowns, and I was usually shocked by how bad they were at that). On the other hand, what both Judo and BJJ have going for them is teaching you to deal with a resisting opponent in close contact.
When it comes to longevity, it also depends - Judo and BJJ have much (!) higher injury rates in my experience than something like Karate and Taekwondo. I do think BJJ is easier to start in your 30ies compared to Judo, though, and you may be able to keep at it longer.
Mobility will be an aspect mostly up to you, in terms of strength and cardio you'll likely benefit the most from Judo, since the pace is the highest among the styles you listed.
If you ask me, I'd recommend rethinking your priorities first: if self-defense is the most important to you, I'd recommend a different route entirely and either enrolling in a system specifically geared towards that (e.g. Krav Maga) or doing your own reasearch about awareness etc. (reading recommendation for starters: everything written by Rory Miller); in terms of learning how to fight quickly by doing a combat sport, personally I think boxing has the steepest learning curve at the beginning, and a year or so of boxing will likely make the biggest difference in how well you can handle yourself physically. You'll likely be hitting quite a bit harder and more effectively than with either Karate or Taekwondo in the same time frame. Boxing also places a great emphasis on distance management, timing, avoiding a strike etc., aspects where I think both karate and Taekwondo are often lacking a bit. From there, you could add a grappling art of your choice, basically creating your own version of Krav Maga (which, incidentially, was founded by a guy who was both a successful boxer and a successful wrestler) or moving on to a different system like Silat etc.
