I don't know if my experience is typical or not but I changed fields 2 years ago and didn't have a problem at all.
I was more than ready for a change after 10+ years in the same "on call 24/7, swing shift, travel up to 5 hours one way" job.
I was actually interviewed and hired three different places (and was able to pick and choose after careful consideration) and in each case the interviewers were younger than me.
My years of experience was a benefit, not a drawback, although one interviewer did ask if I was prepared to take an entry level position after being in Management for years. (I didn't have a problem and have moved right up in the last two years - it happened to be the job I chose)
I just turned 50 this last August, if that helps at all.
I was a little worried because when I first started hunting I wasn't getting call backs at all but I think, in retrospect, they were positions I wouldn't have been terribly happy in, anyway.
Good luck on your search!