I've found that just telling them, up front, that I'm over 40, terminates the relationship almost immediately. They can't hang up, fast enough, and I never hear from them again.
My secret is to learn and know "enough" about every OS, every language, every framework out there. Of course you're starting and you don't have either the time or experience to do everything, but do it anyway, slowly, one task at a time. Compare, study a bit, read, and have fun. Also, don't be scared, no one knows everything, you just need to know enough to be able to help (and learn at the same time).
You may need to kick open a few doors. I probably could have done that, but I couldn't be arsed.