First of all, 26 is not old. It's just not.

on many nights I end up vegging out in front of the TV or aimlessly clicking around on the internet.

An hour or two per day of that is not a big deal. You need to relax. As long as you're doing well at your job and getting enough exercise, it's fine to watch an hour of TV. One warning: assume that once you start watching TV or junk internet, you probably won't do anything else for the rest of the day, so don't start until you've accomplished enough that you'd be OK with that. Also, keep a set bedtime. The problem with staying up late with TV or junk internet is that your judgment gets worse as it gets later and you're not as good a judge of "Is this really more valuable than an hour of sleep?" at 12:00 as at 10:00.

You shouldn't beat yourself up over needing an hour per day of "do nothing" time. That's completely normal.

I am crippled by the feeling that it's "too late".

As Ed Kmett says in this very good (and accessible) talk on how to learn (link: https://yow.eventer.com/yow-2014-1222/stop-treading-water-le... ) your career is going to be a lot longer than you think. It's far from too late.

Every day, I read an article by some hot-shot young dev who has a handful of fancy projects behind his belt (not to mention a great website and design sensibility) while I have exactly zero

Well... a few of those people were just single-minded and focused, but many of them were also produced. Evan Spiegel's a billionaire at 24, but he's a product. He was picked by aging venture capitalists, facing irrelevance and acting out of fear, to match their idea of what Millennials look like. Twenty years from now, these products (Lucas Duplan, Evan Spiegel) won't be relevant. Take the same attitude toward those "30 Under 30" lists. They have the same problem as the "holistic" component of college admissions: they're middle-aged C-players trying to separate the A+ from the A players among the young. (The middle-aged A/A+ players are out kicking ass and therefore too busy to give a shit about "30 Under 30".) They're just not capable of making meaningful selections, so you should view it as irrelevant celebrity noise and ignore it.

Trust me that very few people half a decade younger than you (that's 21) are producing fundamental work. Young people do get a lot more recognition for accomplishments that would be mediocre by an adult standard, and those "golden child" types get addicted to the recognition and don't improve. The people your age who will be kicking ass 20 years from now are, most likely, not even on your radar right now.

Some young people are producing fundamental work, and that's awesome, but they aren't numerous enough to represent a competitive threat. The people who are producing fundamental technology are generally not peaking in their 20s, but 40s to 50s and sometimes later. You have time to catch up. Some people have incredible focus even at 17; most of us take some time to get our shit together and that's OK. Fuck, I had a 9-year trolling habit (17 to 26, or 2000-09).

Whenever I encounter a technical article, I immediately and compulsively investigate the author's age.

Stop doing that. If you can't, see a psychiatrist. If it's an actual compulsion, then medication will help you.

For the first time in my life, my procrastination is starting to get tamed.

It will probably continue to get better. The ability to plan and project yourself into the future is sub-optimal from ages 12 to 25. In other words, it's normal to take that long to get your shit together.

But I can't help but feel that if I had started in earnest at 25, at 21, at 19 — then maybe the list of accomplishments at the end of my life will be longer.

Who knows? It's not worth fretting. You know kids who are straight-edge rule-followers in high school and go completely apeshit (and not always funny apeshit, but sometimes scary apeshit, like the guy who got to a near-fatal 0.37% BAC) with the first taste of freedom in college?That happens a lot to people who are "on the rails" in their early 20s. And the ones who get huge amounts of recognition (e.g. "30 Under 30" types) tend to fall the hardest because the recognition from "above" gets them used to looking up, and when they actually have to lead, they're not up to the challenge.

Does anybody else have this problem? How do you deal with it?

Look, everyone has these insecurities. I would be lying if I said that I didn't. It won't prevent you from doing a good job. Just get out there and build. Don't expect the insecurity to go away; just work in spite of it. From Game of Thrones:

Bran: Can a man still be brave if he's afraid?
Ned: That is the only time a man can be brave.