This is my daily driver, a 1992 Trek 820 in electric blue with black spatter. I got it for free from my brother about a year ago, and have since put ~4K miles on it. I have another 820, and I love these bikes. They make great city bikes. They're dirt cheap, geared well for the hills in my area, and they just work. It's nice to have something in your life that you don't ever have to even think about. I've made some upgrades for my use, including the racks, basket (I have a second I attach to the front rack for Costco runs), fenders, street tires, and high rise handlebars.
How is the frame doing - for its age? What material is it made of?
Looks like a steel frame.
The neat thing about steel is that it has an infinite fatigue life as long as you keep it out of the plastic deformation range (unlike aluminum and other metals, which will always eventually fail under repeated loads, no matter how small the loads are).
What this means is that as long as you never put the steel under so much stress that it gets permanently bent (and you don't let it get rusty), it can continue being used forever. Literally forever. As long as you don't abuse it, as long as you keep it clean, dry, and not rusty, a steel frame will never fail from fatigue and age. If properly cared for, a bicycle frame like this one could keep going for thousands of years and work just fine.
Honestly, steel is a really awesome material for engineering, and because it's relatively cheap and plentiful, it often doesn't get the recognition it deserves for its amazing material properties.
I missed a golden opportunity to order a stainless steel frame from a small company. They gave lifetime warranty on the frame. Sadly, they don't build it anymore and the company dissolved. I am a great fan of steel, too, yaknow!
Aluminum is hard on the ass and Carbon makes those cracking noises that cost 5K each time you hear one. Steel is the metal to beat for service life.
It perfect. The main tubes are chrome moly steel.