Hi this is a question that has bothered me for years.
I can understand why, it's a vitally important issue.
Ok, seriously, I haven't worked in many different places as a Progress programmer, but when I have the ages have ranged from undergraduate placement (19/20) to 30s for full-time employees, contractors normally older.
So 18 is pretty young (for countries where post-18 education is normal), but only really because most places demand a degree before employing programmers. Some geeky types get work while at school, and before programmers became a dime-a-dozen, it was quite normal to get a job programming straight after leaving school, rather than going to Uni.
It's arguable because Progress is niche (ie. not known by people who don't take an interest in their industry), and not perceived as dynamic and new-bright-shiny, it won't be first on the list of most young, thrusting know-it-alls, and I suspect a lot of programmers fall into it by chance (like me).
My own, unsubstantiated, suspicion is that Progress 4GL programmers are likely to be an older demographic, not least because Progress is way behind the times in keeping the core language up to date with modern approaches, and for the aforementioned niche reasons creating a lesser appeal for bright-eyed young graduates.
The more recently aquired branches of the company are a little more edgy, the messaging, event processing sides, so maybe one day Progress won't have a reputation amongst people vaguely familiar with it at odds with its name.