The Biggles fan may well have been me, as I unashamedly am one (of the war stories at any rate, not so much the later
Biggles: Special-Giant-Crab-Fighting-Air-Detective variety).
He does age a bit, as he is clearly a teenager in some of the books set during the Great War. I don't think he's described as such in the WWII books.
They were originally written as books for young boys, though I still find them entertaining. But then again I'm pretty immature myself. Despite the age they were aimed at they have many references to alcohol and smoking (though hardly ever romance, and never sex) which were actually edited out in later editions. Happily they're back in the modern ones.
Here's quite a good site for Biggles fans, which shows how many were written (and how far they veered from the original Great War Dogfight theme):
http://www.biggles.info/