I am in a similar stage. I have a SUV spare tire. And, I am flexible as a plank.
I just started biking seriously about a year ago when I turned 42.
For my first serious road bike, I had a bikefit done with the fit set up so I would comfortable on the hoods and bearable in the drops. This translated to +40mm head tube spacers (from the Chris King inset headset with 12mm of stack) and a 100mm stem with the Enve compact handlebar (I can't remember the drop and reach). The bikefitter told me that I should ride more to increase my core strength and do stretches and yoga to increase my flexibility. The bikefitter asked me to come in for a bikefit tuning every six months.
Currently, I ride about 250 miles a month and stay on the hoods 80% and in the drops 20% of the time. My cadence is 85-90 while I am on the hoods but drops to 80 while I am in the drops. Every week I try to push this envelope a bit more - to the point of being slightly painful and uncomfortable. Hey, no pain no gain.
With my current responsibilities, I probably will not be able to ride more than 300 miles a month apart from special bike/beach vacations, where I would put my family into a beach bungalow with room service while I ride.
The bikefitter told me that the goal, within two to three years, is to decrease the head tube spacers to +1 cm or less and to increase the stem length to 110mm or 120mm. The bikefitter races and probably rides more in a week than I can ride in a month. I am almost double his age - my goal is to just have a good time riding and hopefully cheat time.
I can not emphasize the importance of a good bike fitting. I have no back pain, shoulder soreness, forearm pain, or knee pain (even with a partially torn ACL) after my weekly 50 mile rides. Of course, the centuries are another matter, starting at mile 80. Soreness because of over-exertion is normal but pain because of a poor bike fit is not.
Cheers.
Mark