I replaced the old O2 sensor with a new one and the light still comes on. The light only comes on after driving for about 15-20 minutes.

Any ideas on what it could be?

solved, thank you for the help!

 

The code 1 does seem to imply that the O2 sensor is bad, but it actually saying that the readings from the O2 are not what the ECU is expecting.
If you have vacuum leaks, exhaust leaks, rich or lean fuel mixture, etc etc. they can all lead to unreasonable O2 readings and pop the code.

Wiring is suspect - especially if you have done a wire tuck or an OBD1 conversion.

 

I still have OBD0 and when I start the car and let it run for a few seconds, I do smell exhaust gases from the front/back? if that means anything. On the highway, my exhaust sounds a bit loud, but I recently replaced my muffler and plugged a resonator with a hole in it, plus my rear is gutted to remove rust.

What are your bets on a bad fuel pressure regulator? I do smell exhaust gases/gas coming in the cabin area from the front of the engine and possibly gasoline, but nothing leaking to the floor. Idle sometimes get rough maybe 10% of the time and my car has nearly 300k+ miles on it. The only time something leaked gasoline was near the fuel tank when I filled up my tank to max. The fuel leaked from some hose near the fuel tank, so I re-adjusted the clamp at the end of the hose

Do you think this is a safe bet to follow: https://manuals.co/workshop/honda/ci...al/5524663/131

 

That flowchart is an excellent place to start.
Rather than just throwing parts at it and hoping for a fix, actually doing the tests can save you time and headaches.

Have you tried popping the hood and snooping around for a leak to figure out where that gas smell might be coming from?
If there is a hose leaking or an injector o-ring that has failed, it could very possibly be your problem.

 

Popped the hood and let it run for 10 minutes. Smelled the right side of my engine bay and nothing. Smelled the left side of my engine bay and smelled exhaust gases. Exhaust did smell like gasoline (or so I think). Didn't see any leaks in the engine bay.