He is a young, albeit hefty, kitten learning how to perfect his hunting skills. Climbing things is part of that process, as well as darn good exercise. Cats can be trained, but not by punishment. You need to motivate them to do what you want them to do, rather than punish them to prevent them doing what you don't want them to do.
So, what does your cat accomplish by climbing the drapes? He gets exercise; he gets up high; he gets to challenge his climbing ability. What you need to do is to give him an alternative to the drapes and then make it easier for him to climb the alternative than to climb the drapes.
You may wish to take the drapes down for a while so that he doesn't have access to them. I don't know how feasible that is in your household and if you could put up blinds in the interim. I would recommend investing in a floor to ceiling cat tree - there are some relatively inexpensive ones available that use a tension pole to brace against the ceiling that have perches on the way up. The cat can climb up and down the cat tree, and if you place it by the window he may well prefer the challenge of the cat tree to the drapes. If you have space, you could also invest in a length of 2 x 4 board (6 ft or 8 ft length) and lean it in a stairwell or against something that is high (ie. cupboards) that so it provides a sloped access between the floor and the higher level surface. Secure it at one end (tying it at the top of the stairwell, etc.) and if you wish, you can wrap part of the 2 x 4 with 1/2" or 3/4" sisal rope (also available at a hardware store). This provides him with another fun surface to run up and down that gets him up high and allows him to practise his climbing skills.
Good luck. He should generally stop trying to climb the drapes by the time he is older, but I fully appreciate you will want to find a way of diverting his energy now :-).