A few things that I wrote as far back as 2000 and 2001 are still in use. Just checked one right now and the login screen is still the same - no doubt passwords have changed, and it says it's running on php 5.5.9 on ubuntu - they've done some upgrades, and I can't imagine the backend is 100% the same. however, the url structure was built to do something funky, and that is still in place, meaning they very likely didn't throw it all out and start over (and the login screen is the same too).

Had another call from someone last year saying "x is broke" and... piecing stuff together, I realized they were still using something built in 2002, and using it 13 years later (now 14 years). Trawling through old code was weird - a mix of pride - much of it was pretty readable and understandable - and regret - many 'cut corners' I wish'd I'd not cut now, as it made the fixes take longer.

That said, I think there's something very useful about having to deal with your own code 5-10 years after the fact. You'll have a greater appreciation for why 'the right way' is what it is, and ime, I've found that code tends to be more maintainable and understandable by others when it's been written by someone who's had to maintain old code themselves (usually their own).

Doesn't mean newer/younger folks can't write good maintainable code, but it's a skill that seems to come with age more than anything else.