You're welcome. I'm not Japanese, so I'll stick to English.
The first step is to go to a class. You may watch, you may join in, each different school will be run differently, so check with them. Ask questions, certainly. If you were in Japan, that would be a definate no, but Western cultures tend to like them a fair bit, so it'll be more accepted there.
As for age, again it depends on the school. I have come across Kendo classes for children as young as about 5, so check with them. In my school, we generally only accept students 18 and over, other Ninjutsu schools have kids classes, so who knows?
Okay, you have "come into possession of a katana/wakizashi set... should (you) see if you can handle it... they're not sharp except for the tip", oh boy. There's a fair few warning signs here in just a few words, so you know. To begin with, what so you mean you came into possession of them? He passed them on to you? Where did he get them from?
You also say that they are not sharp except for the tip... how do you know? Did you try cutting with them, or did you run your finger along the edge? If you answer yes to either of these questions, DO NOT DO IT AGAIN! The blade of a Japanese Sword can be easily damaged by the oils in fingerprints, resulting in rust-prints on a blade. Don't touch the blade if possible... at all. I cannot under-emphasise that. And if you attempted cutting without instruction, you are asking to hurt yourself. Don't.
If you know because that is what you were told, then that is a different story. There are a couple of different swords that are unsharpened, but retain a relatively dangerous tip (kissaki, if you want the Japanese...). At the top of the scale is a Mogito, which is a real sword that is unsharpened, then you go to Iaito, which are baldes made from a zinc/aluminium alloy, to soft to take an edge or hold up to the rigours of contact. Lastly you have the decorative trinkets which don't deserve the name "sword". They are sword shaped pieces of metal, with no balance, no integrity, no edge in the sense of a real sword, and are just imitations. No use at all. If your great grandfather gave you one of these, be dubious about it's origins...
If and when you join a school, it will be a while before you get anywhere near a real sword, or even an Iaito (in most cases). Typically, you will begin with a bokken (or bokuto, a wooden sword) until you have the requisite skill to be trusted with a metal blade. Remember, the concern will be the safety of those around you, not your safety, so you need to demonstrate that you can control and (most importantly!) STOP a sword. Then you will begin to use a metal sword, and after a while of that, eventually a live blade.
Don't be too eager to pick up a real sword. They are dangerous items, and should be treated with respect, and only picked up by those ready to use them. But don't worry, you're young, and have plenty of opportunity ahead of you!