In what sense? Age? Technical knowledge/ability?

I know a programmer in Austin who makes his living in FORTRAN. I'd imagine if he loses that job he's pretty much SOL except for a few niche positions which are likely filled already.

Most of the defeated older programmers I've talked to feel that it is a young person's game and they don't want to have to relearn something new and come back as a junior. Quite often it seems like something simple that that is holding them back, like not having knowledge with jquery or more UI tools, or not knowing how to work in linux.

But I've never been unemployed for over a year and I have no idea what that does to your confidence.

Going back 25 years: It doesn't do much for your confidence at all.

My way out was voluntary work, lead to engagement with a lot of different people in local voluntary sector, lead to a paid post, which, in turn lead to a teaching job. I could see what Further Education college teaching was like from my work with trainees, and I realised I could do that.

Never been out of work since...

What transferable skills do programmers have that could be used in different fields?

I think it's an incorrect assumption that you'll be coming back as a junior (on their part, not necessarily yours). Senior Devs learning new skills do not get bumped down a pay grade or more, with the rare exception that their old skills are totally worthless.

I think the idea that 20 years of experience in mainframe hardware warrants a senior or even mid level web development jobs is just as misguided as the idea that a college degree warrants any job just by virtue of having it.