I've loved my Felt Z for the past 15 years or so (I'm 70). I don't even know if they market a Z nowadays, but I'm pretty sure they have an equivalent. It didn't slow me down one bit from my Cannondale CAAD8 back in the day. There's a lot of bikes with more "comfort" geometry, aluminum, carbon fiber, titanium, steel. But, look beyond Trek and Specialized, please. It's a big world out there with many great options with equal or better value. They can be built up as light as you want, certainly 15 pounds in a rim brake bike is pretty doable if that's your goal.

If you're looking at used bikes, don't have tunnel vision towards disc brakes. For road riding - in my personal experience - discs don't add anything to the performance of the bike. Not worth getting obsessed over. I have one - a titanium gravel bike, and it's fine, but my rim brake bikes work perfectly all the time too.