I'm sure there is an operation you can get done to either get rid of it or certainly reduce it, I think I read that somewhere a few years ago. I think it was Shaun Palmer that had it done when he did DH. Correct me if I'm completely wrong!
I ordered a CK headset from America, it took a bit of time to arrive but I didn't need it right away so that was fine. It worked out a fair bit cheaper than buying one over here.
Your never too old to ride trials. Hiroshi Hirano (President of Biketrial International Union) still rides and he is 52!!! You can read a bit about him in the new MBUK.
I clicked Yes even though I haven't ridden for about 2 years now, but I do have a new bike on the way, bit by bit. The hardest part of getting back into trials for me will be building the confidence to go big again.
He asked "which should I ride", you have just suggested all 3 sized trials bikes. I dont think that will help him very much. I would say you have to go for what ever type of bike you feel most at home on, which I would suggest is a 20".
I watched the first series but havn't seen any since, so I think I would be "lost" if I were to watch some from this series. What series are they on now anyway? 3 or 4?