I think it's real scarcity. I'm 41 and am always one of the oldest in any group of devs (except for that Usenix event I attended :-).
Most people get into their career in their twenties. For computers it's often even younger. But it seems relatively rare for someone to pick up programming in their 30s or older.
If you're 40+ today, your twenties were ending around the time that the "tech boom" was beginning. But there just wasn't as much information and inspiration around for getting into software development. Even through the mid-90s a college degree and programming skills was no sure ticket to cushy employment.
Or just so obsessed that you stayed in programming even when it wasn't obviously a good idea. Come to think of it, it's still not obviously a good idea.
