I took up martial arts around your age and did it pretty seriously for about 15 years. I’d recommend it. But don’t be stupid like me. I stopped mainly due to 2 injuries. Shattered my left wrist just throwing a sloppy hook into a (thai) pad - then proceded to train/fight with the broken wrist for a couple of years. Then repeatedly hyperextended my right big toe during BJJ/grappling. Again, continued to work out/compete without getting any treatment.
Training full contact involves some real risk of injury. But IMO you need at least some full (or close to full) contact work to truly develop any ability.
IMO if I were to train one martial art for practical self defense, it would probably be boxing. You will encounter VERY few people who can successfully deal with the combination of quick hands, power from both sides, excellent footwork, and evasion - which are the keys of boxing.
Unfortunately, one aspect of learning to defend yourself is learning to recover after being hit. It is a pretty unigue experience to take a hard shot to the head or elsewhere, and realize that you HAVE to avoid taking another shot like that, while at the same time trying it inflict as much injury on the other guy. Also, to some extent taking a hard shot gives you the surest feedback on how hard your shots feel to the other guy.
Having said that, a lot of boxing gyms teach boxing irresponsibly. Rather than spending endless hours up front on mechanics, they tend to toss guys into the ring too quickly. You can get a TON of benefit from “sparring” at 1/2 or 3/4 speed/power, limiting targets to below the head, or imposing other restrictions. Learn how to wrap your wrists correctly. Buy and wear good quality gloves, mouthpiece, and headgear.
For pure fitness, I’ve done marathons, trained and competed in boxing, kickboxing, BJJ and NHB, and done a lot of other demanding things, but I cannot think of anything I’ve done that was more demanding than our workouts that simulated 10 3-minute rounds with 1 minute off in between. The combination of physical exertion, combined with the mental effort of trying to hit while avoiding being hit - and keeping that up when exhausted - is unlike anything else I have experienced or could imagine.
Speaking of krav maga - I’m a big fan of mixed martial arts. The guys I used to work with were more along the lines of JKD/FMA/BJJ, but similar idea. But realize that with everything there are good and bad instructors/schools. Right now at the gym I work out there is a guy who works out regularly on the heavy bag. Works REALLY hard, and wears t-shirts that say krav maga. But seriously, if that poor boy wanted to train at how to get the shit kicked out of him, he’d have a hard time doing better. Every punch is telegraphed, and he consistently drops his guard. Unless he has the doubleleg takedown of an NCAA wrassler, any moderately skilled boxer would take him apart.
Also - be very wary of cardi-kickboxing. A rare few are conducted by folk who know how to box/kickbox. In those classes you can gain some real skills in addition to fitness benefit. But IME by far the majority of such classes are taught by folk with little or no experience with effective boxing/kickboxing/self defense. Not that they aren’t fun classes or good for you. Just don’t think they are training you to be Bruce Lee.