As others have noted, your build is irrelevant to your choice. Any of the arts you mention will work just fine for someone of your size, age, and condition.
The general answer to these "which art should I choose" posts is always the same. Visit as many of the available schools as you can. Pay attention to the general atmosphere, teaching style, schedule, location, and costs. You might find the best art in the world, but if the teacher doesn't click with you or you don't enjoy the atmosphere or you can't afford the tuition or the schedule or location are too inconvenient then you won't end up training consistently.
I can give you some general ideas about the experiences you might find in the arts you list and how those might translate into improved fighting ability. ("Self-defense" is a broader, more amorphous term. Most self-defense is not fighting and most fighting is not self-defense, although there is some overlap.)
Wing Chun: WC is a specialized art focused on close range striking. It has some good physical principles and can be effective. However many schools do little or no free sparring and focus almost exclusively on stylized drills for countering other WC practitioners. Without sparring and pressure testing against non-WC stylists, a practitioner is likely to fall apart against a tough opponent.
Boxing: A good boxing gym is one of the fastest routes to solid unarmed fighting skills. You'll gain good physical and mental conditioning, the ability to hit hard and non-telegraphically, the ability to evade punches, good footwork, and the ability to not freak out when you get hit. Downsides - very limited grappling (just some basic clinching) and you won't work on preventing takedowns or how to protect yourself on the ground if you do get taken down.
Muay Thai: Much the same as boxing, except that you will also learn kicks, knees, elbows, and solid clinching skills. The wider range of skills covered means that you will have less practice time to refine your punching and footwork to a high level. Depending on where you are located, the available Muay Thai instruction might be anywhere from mediocre amateur to world-class professional.
BJJ: Primarily a grappling art, specialized in ground fighting. Any legit BJJ school will get you in great shape and help you develop excellent ground fighting skills. The thing to watch for is whether the school has retained the self-defense curriculum: punch defense, takedowns, standing clinches, dealing with common real world standing attacks. Many schools these days have started to focus almost exclusively on sport BJJ, which is mostly about grappling on the ground. A lot of the sport applications can carry over into self-defense ... but not if you can't defend against strikes and get the fight to the ground in the first place. If you can find a BJJ school which devotes a good amount of practice time to dealing with strikes and stand up situations, then this would be an excellent option.
Judo: The parent art of BJJ. Primarily a grappling art, Judo focuses more on throwing an opponent to the ground. Judo does include ground grappling, but it's typically not as developed in that department as BJJ. Pros: You'll get in great shape, you'll learn how to throw people around, you'll learn to fall without being hurt (one of the best self-defense skills out there), you'll learn to keep from being taken down, you'll learn enough ground fighting to handle most untrained opponents easily. Cons: In most schools you won't get practice defending against punches. If you have the option of studying both boxing and Judo, they make a great combination.
Karate: There can be a huge degree of variation in what you find in different karate schools. Some focus heavily on physical conditioning and full-contact sparring. Some focus on solo forms as performance art and tippy-tappy tagging the air sparring. Some are all about kata (sequences of techniques performed solo) while others do no kata at all. Some are just focused on striking. Some have a blend of striking and grappling. Some instructors have a solid understanding of unarmed fighting. Other instructors are clueless and delusional. You have to check out the individual school to see whether it's worthwhile.
Hope that helps. If you can provide links to the websites of your local schools we might be able to spot any potential red flags.
