First off, a massive congratulations to you on your first web developer role! OUTSTANDING! There are dreamers, and there are doers... and clearly, you are a DOER. BRING IT... I'm getting motivated just thinking about how hard you've already worked in the lab to GET TO WHERE YOU ARE NOW!

I'll try to hit most of your key points:

1. "[...] at the age of 33."

I would encourage you to forget about age. It's just a number. In reality, the clock is ticking for all of us, so I think it's more important to focus on right now. Work to live in the moment. Some started early, some started late. I'm older than you, and I just published my first game for iOS in January, in Swift, which was an entirely new language when I started with Xcode 6 Beta 1. So, again, it's just a number. You are bringing the thunder RIGHT NOW, and that's what matters. I can't stress this enough. Sure, wouldn't it be grand if you had started on a Commodore 64 when you were 12? Well, that's not the case, so you do what it takes, you do the work [1], you build that wall of knowledge brick by brick, and you make it happen for yourself.

2. "I now spend my days feeling overwhelmed and struggling [...]"

To be honest, you're not alone. When you are learning something new, this is the nature of the learning curve. You just have to keep building that wall, one brick at a time. Do the work. It's the only way to move forward, the only way to hone your craft. You have to keep driving through.

3. "I annoy everyone else (who are all about 10 years younger than me) with my constant questions."

There is nothing wrong with asking questions. However, you have to know how to ask the right questions and work within the schedules of your colleagues. That is to say, the right questions are, for example, questions about the project, the architecture of the system, etc. For these, work to carve out time with the colleague(s) that can answer these questions, so that you aren't hitting them up in a way that breaks everyone's flow. The "wrong" questions, if you will, could be, "How do I do X in language Y?" Those types of questions are best answered by you doing your due-diligence and off-hours study.

4. "I find myself filled with regret that I didn't start this career earlier [...]"

See point 1 above. We've all played this game. We all have regrets. I wish I would have had kids earlier than I did, for example. But, guess what? I can't change the past... I can only drive forward and GAIN GROUND. So, you'll never win the "Regret Game." You can't win against yourself. Dr. Seuss said it best in, "Oh, The Places You'll Go!" (Please read it if you haven't; it's absolutely wonderful.) Here's the quote: "I'm afraid that sometimes you'll play lonely games too. Games you can't win 'cause you'll play against you." You are striving to evolve and striving to do the best that you can, and any decision that you make will ipso facto be made with the most up to date and diligent decision-making faculties that you can muster at the time. Therefore, you were right for what you believed to be right, in the moment that you made the decision, and that is all that will ever matter; strive to let go of the anchor of regret.

5. "I'd seriously consider quitting if I had anywhere else to go."

I would encourage you to keep grinding, keep learning. You have to embrace the grind. I know it's rough. I've been there; I think we've all been there at some point, to be perfectly honest. But, in some sense, if you do leave, you may find yourself at exactly the same place, in the sense that... yes, you may be in a new job, with new people, new surroundings and perhaps new geography, but you will still be the same technically, that is, struggling to get your grounding and learning the craft. So, it may feel like changing will help, but I would encourage you to carefully evaluate that decision before taking any action.

I wish you all the best.

[1] https://news.ycombinator.com/item?id=7076143