I can feel the tl;dr building already.
(correction EPIC tl;dr)
Anyway, the dream hasn't died quite yet, but it certainly has morphed along the way.
Background:
Coming out of high school, I really didn't have any specific inclinations. I went straight into university undeclared and drifted into Physics because I like science and have a decent head for math. But I didn't do shit as far as the work went, so even though I'd pick up and understand everything perfectly well from lectures (when I went, having nobody else being responsible for me getting up on cold mornings was not a good idea), not doing homework really does have consequences beyond just not getting those points. So basically after 5 years of futzing around, I only had 2 1/2 years worth of the degree.
So for work I drifted into retail, where I was pretty good at my job, reaching assistant manager at each company. I overall enjoyed it, and I have to say it was really useful with overcoming a crushing shyness I had when I started (also helped by a required speech class at uni -- I really did get a lot out of the general education classes). But after 9 years at Borders books, I became too expensive to keep under a new austerity program to pay off crushing debt, so they found an excuse to fire me. I'd really like that to be the last of retail for me, but it's the most likely fallback job for the foreseeable future.
The Dream:
This came late for me. During uni, I read a lot of Star Trek novels along with some other sci-fi and fantasy, and at one point I thought "I can do this" so I started writing a Star Trek Novel. Not fanfiction, this was intended from the start to be something publishable by the company. Soon after, I discover the various science fiction magazines, buying and reading about 120 (with about 1000 short stories in them) of them when I ran across a box of them at a charity book sale. The same thought hit, "I can do that" so I started writing a story. I had also just gotten online, so I was able to discover a couple of writing communities where I learned how and where to submit my stories. I also found out that you had to already be a published writer to write Star Trek books, so that part of the dream got put on indefinite hold.
Somewhere in the middle of all this, I had a vague interest in music production. I had played sax in high school, and with money from my first job I picked an old Yamaha DX7 and a 4-track cassette recorder and subscribed to Recording magazine for a while. I've fiddled around with this for years and now can do decent recordings to my computer, but I'd hardly call myself a musician or an engineer. This becomes relevant later, though.
So I wrote, intending my work all along for professional publication, but I still never had that burning desire that drives other writers to get up at 5am because that's the only way they can find a free hour to write between job and family commitments. But I learned the craft fairly well, and I'd say that when I do sit down and write something, it will be at a professionally competitive standard. I also went to the big sci-fi conventions that have a lot of writers, so I've met, hung out, and have become good friends with people at all levels of the industry, from talented aspirants, to award winning pros and editors. I
have the kinds of connections that most people could only drool in envy over. But for the most part, I recognize that I'm mostly talking a good game, so until I feel I've committed myself to writing something worthy, I don't pester these people for favors I can't yet use.
What this has done, however, is allowed me to observe friends who have reached every stage of the dream. Some have already "made it" and are making a living off of their writing, others are being published, but still need a day job and/or a spouse to fill in the rest of their needs. Some have achieved publication, but then faded away again when their works failed to sell enough. One close friend was successfully selling TV scripts, comic scripts to Marvel and DC, and a novel, but burned out so much on the politics of the industry that she dropped it all and only writes for fun now. Most of my friends have been writing and submitting for years without much success, and just drift away from the dream eventually.
So I'm brutally realistic about what "success" in my field means. But I still think I can do it, and the serial novel I've been posting on the boards here is an attempt to reboot the spark inside (getting back to that this next week, btw). One thing about writing is that it never is too late to start or restart. Many of the writers who have won the "Best New Writer" in science fiction/fantasy have been in their 30s or 40s. So this is the main answer to the OP.
Another answer is that I've discovered that helping other people achieve their dreams really means a lot to me. For a while, I had my own fantasy fiction webzine, and finding the right stories to publish out of the hundreds of submissions was immensely satisfying to me, particularly when I found out it was the first sale for that writer. I'm very good at writing, but I feel now that my true calling is as an editor. I
understand story at a level that has led a lot of my professional writing friends to seek my advice when they're stuck. The problem is that I have no idea how to break into this side of the field without the kind of credentials it would take years to build.
But this leads me to the next stage. When I was fired at Borders, it gave me the free time to help one of my coworkers with her music. So I took classes at the local access TV station, made a show featuring her and her music, and now I'm not only continuing the show with new artists to showcase, I'm in school again taking more classes where I can maybe make something in this field my career. The dream would be making music videos, but even if I'm just a camera guy on the local newscast, I think I'll still do what I can to help local artists out with live clips, video features, music videos, whatever.
Finally (finally!), it sounds corny, but I try to be the person who believes in other peoples' dreams. It's sometimes very lonely wanting something that most people around you don't understand, and sometimes all it takes is for a friend to ask what you're working on and can they see it to provide the motivation to take that next step.