43 here and making the switch. I left Web Design about 10 years ago to pursue other interests. However, I'm finding that my current job has pretty much plateaued, there's no "up" to work toward, and what I'm doing now is what I'll be doing in 5, or even 10 years, with maybe a slightly larger paycheck. To see my future there, I need only look across the room at people who've been there for almost 20 years, doing the same thing they did when they started, with nowhere to go. That's not the future I want, nor see myself in.
I realize I've out-grown my current job, and am capable of much more than I'm doing right now. I've been thinking about it for a while, but it struck me recently that I'm 40-something, am not getting any younger, and need to make it happen "now", rather than burning even more time thinking about it. So here I am.
I've decided to return to the Web world, but as a Front-End developer this time, rather than Design.
I've considered the "ageism" angle, as well. But at the same time, I realized that my work should speak for me, not my age. Also, as others have noted, with age comes experience, wisdom and perspective that a younger, more reckless and "energetic" me wouldn't have had. I'm more grounded and focused now than I was when I was younger, and I feel that can be a huge benefit to a company.
And frankly, a company that wouldn't hire me based on my age, and not my demonstrable knowledge/skills is probably not the kind I'd want to work for anyway.
So for me, it's a non-issue. What nibbles at my thoughts is, while I know it's a ways off, yet, "when will I know I'm ready to start looking for work and can realistically expect to be hired?"