Hi Ludwig,
All the above advice is good. I'm in the same boat (so to speak), 40 plus and just had my first lesson the other day. I wasn't going to have any lessons and just buy a board and figure it out myself. Bad idea! Within 10 seconds of the lesson I realised this is a sport where lessons will save you many wasted day teaching yourself bad habbits. With a good instructor you could be up and running within a few lessons- assuming you're fairly fit have decent ballance.
Tip- Pick a nice calm day for the lesson! Over 8 knots and you'll spend most of the time in the drink...lol
Just have have fun mate. Practice on the huge learner boards for a while then down size as your ballance and skill set improves. That's my plan anyway