I got interested in making levels when I was kid, creating small levels of flash 2D games. When I was a young teenager, I got interested in Serious Sam editing and that's where I learned basic terminology of building 3D worlds. I never got anywhere but instead made what would be compared to as small test maps.
UT 1999 was a big game for my friends and myself so I tried to learn to make a few deathmatch maps...again never getting anywhere.
I loved the Quake atmosphere and always wanted to make maps for the game. At some point I tried to use World Craft (or was it radient?) but simply couldn't handle the learning curve or at least I didn't want to output the efforts required.
For some reason, I did a playthrough of Quake 2 years ago and decided to see if there were any more current mapping tools. Enter Trenchbroom and the rest is history.
So I suppose I'd like to extend my thanks to Sleepwalkr for the development of Trenchbroom for it's why I can satisfy my desire to create maps in Quake!
Why am I still mapping? Well with the knowledge I already know, I can actually create maps from ideas in my head. As I continue to make maps, I get a little better at it each time and that's motivating for me. But perhaps the most important factor is that it's really fun to create a world!
I like making maps because I've always liked building stuff. I'm a very artistic and creative person by nature and I've always been attracted to beautiful craftsmanship (either real like buildings, sculptures or jewelry, or virtual like maps or models). I have huge respect for artists and creators and it's one of the main reasons why I intensely dislike breaking stuff. I never vent my anger on objects or furniture, for instance. I'm actually rather interested in becoming a jeweler and a women's undergarment designer these days, since these two things are meticulously crafted and quite amazing to look at (and are a relatively realistic career prospect for me, since I'm awful at everything else).
I started getting into level design at around 9 with Warcraft 2, making maps so me and my neighbors could play new stuff. I quickly became pretty good at it too. Granted, the editor was insanely simple but making a good-looking map in this game does require a bit of work.
My first 3D map was made for Quake, a quite shitty multiplayer level I made at about 11. It was mostly an unlit garbage killbox. It's long, long lost so don't ask for it. I then migrated over to Counter-Strike and Unreal Tournament when I was old enough to have access to the Internet, and mainly made maps for my online friends. I ended up ditching Unreal Tournament mapping for Half-Life/Counter-Strike as I found it much easier.
I migrated over to Half-life 2 when it was released and my levels got enough traction that I was noticed by a few people and landed a gig in the industry. It was alright for a while but a combination of various things and especially high stress made me realize that just wasn't for me. Besides I really hate modern level design (both in theory and tech-wise) so I've been mostly making levels for old games for a few years now and have zero interest in mapping for games that rely far too much on meshes. I remember how disappointed I was when I opened the UnrealED that came bundled with UT2004 and realized how the maps were made.
So, right now I'm 26, I have been making maps since I was 9 and I still love doing it. I feel like I improve every time. That said I don't see myself working in the games industry ever again. I like the limits imposed by the jams and other contests since there are no real stakes and people aren't out to exploit you.