First up, 20 is not too late at all too take up martial arts, so, don't worry about that.
I would say this about choosing a martial art in genral for self defense, full contact vs. no/light contact is what it boils down to. I have tried several martial arts throughout the years. I have consistently come across this same theme over and over with self defense.
I have tried/sampled these no contact or light contact martial arts: Tae Kwon Do (the light contact point sparring variety. There are some that are full contact like the Olympics this is different), Tai chi, Aiki Jijujitsu, Aikido, and Japanese Jujutsu. These arts do have something good to teach you, technically.
I currently am taking Japanese Jujutsu. In JJ we don't have regular sparring and when we do it's light contact and very controlled. They do this for safety reasons and not to "water down" the art (and make it more sport like). I learn some good moves in there. But, I never have full contact sparring to tell me how well it would do against somebody trying to stop me from doing that technique and fighting me back at the same time.
This is the problem with no contact or light contact arts. You never get an idea of how a real fight is. A real fight makes you scared, takes endurance, strenght, pain resistance, a competitve fighting spirti, courage, etc. You don't experience this or don't experience it well enough in these type of martial arts. You can learn some great moves and, yes, you may be able to pull them off for self defense. But, you won't know very well ahead of time how well you will do in a streetfight struggle for survival withought full contact sparring and/or competition.
I have taken full contact martial arts: Kickboxing, boxing, jeet kune do, judo, brazillian jiujitsu, and submission wrestling. They all have sparring and competition where you use your moves full force against some resisting you and fighting you back. This help tremendously in learning your moves and how they would realistically work in self defense. You see where you are weak and where you are strong, all ahead of time. So, if you do get in a self defense situation, you have some idea of what you can and cannot do, what probably will work and probably wont. You already experience through sparring and competitions stuff you will face in self defense probably: fear, fatigue, the desire to win or lose, pain, etc.
These martial arts are definelty harder than the other type. It requires getting in good physical shape through strenous exercises, being competitive with others (in a good sportsmanship type of way), shrugging off defeat and improving, coping with injuries and pains, etc. The other type are sooo much easier on you. It some ways the "softer" ones are more fun. But, if you want serious self defense, the "harder" ones will make you pay a price for it and then, reward you for it!
I currently take Judo and Japanese Jujutsu. It is both a "hard" art and a "soft" art. I started with Japanese Jujutsu just to get me back into martial arts again after a layoff. But, that no/light contact sparring wasn't going to cut it for serious self defense by itself. I am learning some good moves, and it has potential. But, I need that full contact sparring and competion I was missing. So, Judo is solving that part. Judo and Japanese Jujutsu are related (since Judo came from JJ). So, some of the moves are similar and have similar strategies. Judo gives me all the advantages of a full contact martial art. JJ gives me that technical knowledge that helps add to my Judo. That is currently how I am handling my martial arts training. I feel it will result in me becoming basically prepared in self defense. But, that full contact training I feel is essential. JJ alone wouldn't cut it.
So, look into all those full contact hard martial arts: Kickboxing, boxing, wrestling, sambo, catch wrestling, greco roman, muay thai, full contact Olmpic style tae kwon do, kyokushin karate, mixed martial arts cagefigting, judo, brazillian jiujitsu, and any others that do some type of full contact. I wouldn't worry about taking more than one right now (like I am doing with Judo and JJ). I would just choose one and go with it. You will get some basic self defense skills you will be able to use for real. You won't have to guess whether they may or may not work. They prove themselves in sparring and competition.