I am 33 as well and have been working in web development for about 10 years. I still wonder the same thing, myself. An interesting thing about this field is tha

I am 33 as well and have been working in web development for about 10 years. I still wonder the same thing, myself. An interesting thing about this field is that although things change constantly, there are concepts that are transferable from one to the other. If you build a good foundation on those things and keep trying to learn new things,your age never enters the equation. Since you already have a design background, I think it would be well worth your while to just learn how to use HTML, CSS and javascript effectively. You should be able to learn them inside and out in comparatively short amount of time compared to something like objective-C. There is also a big market for designers who can work with code (script?).