After 20 years doing a mix of embedded and application development, I spent 5 years teaching English. I went back into IT at the age of 45. My first interview was absolutely horrible (sorry about that if you are reading ;-) ). After that I was fine. I ended up getting a web development position without much prior experience in the area (just whatever I had hacked around on in my own time).
Of course with 20 years of development experience and 5 years of teaching experience, I had a lot of other things to sell as well. I certainly had no lack of interest and had positions to choose from. I did take a fairly healthy cut in salary, which seemed reasonable to me since the company that hired me was taking a risk. I was careful to pick a position that would work well for me and I did not take the highest offer. I definitely feel that the investment I made at the beginning was definitely worth it.
I think as an older person moving into a different area you have to be able to convince people that you will pick things up quickly and that your other attributes are worth it while they wait for your technical skills to come up to par. If you are careful to build the kinds of skills that will be valuable throughout your career, you will have relatively no problem in my experience. The people who have trouble are the ones that were just scraping by in their original positions, or people who had a laser focus on a particular skill set that is no longer valuable.