I'm level 2 Green Belt. Best way to learn it is to train with an in structor and a diverse group of training partners so you have experience fighting people of different shapes, sizes, reaches, hand speeds, hand accuracy, and strength. I understand your gripes about the middle-aged instructors, but I've had some of those visit my school and you can't really judge them on appearance alone. If you give me some insight on where your located I might be able to find a good school for you. Hell some people who come to my school have to drive an hour but they suck it up because they want to learn. A lot of Krav Maga schools teach basic self defense, but try to look for schools with instructors or owners with law-enforcement or military experience, as they can give you an even more depth experience and education. As for the long term-trip to Israel, that's good for learning the material but unless you find a place to practice it here in the U.S. or wherever you are afterwards with training partners and instructors, you'll get rusty, and you don't want that to happen with a skill like this that your life could depend on.
As for the traveling to third world countries, its important to have the knowledge but just know that while you should always be prepared to fight and go from 0 to 100/ lethal force, some situations are much better handled with complacency, especially if you are abroad. E.g, a guy who gets in your face, in a dangerous country, in a bar where the guy who looks like he might possibly be acquainted with other patrons or the staff, isn't worth getting into a fight with. (You should watch your surroundings and move with your back facing the wall around the perimeter of the room until you can leave safely. If someone already throws a strike at you put your hands up immediately and get into a fighting stance, and judge who/how many attacker are coming, and decide whether to fight or flee, but the important thing is to have your hands up for an immediate defense or counterattack.)
There are 3 other pieces of advice that slightly extend outside of Krav Maga training I would give to a student:
-Always carry a weapon with you whether it be a knife, taser, gun, or steel toed shoes, it's always good to have an ace in the hole (so long as you're not in a foreign country that's legally inhospitable for visitors, then it gets fuzzy)
-Learn how to fight with random objects in your surrounding; "Krav Maga vs. Someone with a bottle" might give you good odds, but "Krav Maga with a Pool stick or Krava Maga with a Cigerette Ashtray vs. Someone with a bottle" I like better.
-If you need to run away from danger learn to sprint fast and learn parkour. Unless you are in a wide open area when attacked, learning how to traverse and climb different objects to reach locations your pursuers cannot is invaluable.
If you have other questions you should be able to find them here:
http://www.kravmaga.com/forum/