59 here. Been back on the bike two years, starting with hybrids. Finally got a road bike this summer, first one I've ridden in more than 30 years.
Hills are my nemesis, always have been even when I was younger and fitter. Some limitations now from asthma, thyroid disease and neck/back injuries, but mostly it's lack of conditioning for too many years. I walked with a cane for years after a 2001 car wreck, so it took awhile to get back into shape. Just had to be patient and persistent, and be satisfied with every bit of progress.
Besides the lighter bike and tires, what finally helped was to emphasize high intensity interval training on hills. I mostly gave up on longer casual rides and since June focused on 10-20 mile rides on nearby hilly routes.
And we don't have much in the way of hills -- mostly 1%-2% grades up to a mile continuously. Some roller coasters with 6%-9% climbs for 50-100 yards, then plateaus, then another short steep climb, then a slight downhill, then another short steep climb, then a plateau... you get the idea. Nothing long and steep nearby. I need to ride 30 miles to the nearest place with something like a 4% climb that goes on for a mile or two.
But my immediate neighborhood has lots of half-mile long 2% grades, so I concentrate on sprinting those. And a little farther away is a 2.5 mile loop with half-mile 3%-5% overall grades that increase to 6% or so near the peak.
On days when I have only an hour to ride I hit those and repeat 'em until my legs and lungs are on fire.
Frankly, some days it's a little boring. Same stuff over and over. But where it pays off is when I do have time for 40-60 mile rides, including casual group rides with friends. On those rides, I can enjoy a 12-14 mph long ride and it feels relaxed. No gasping for breath on every little hill, or sprints across intersections to beat the light, or to catch up and close the gaps when a large group goes into the usual accordion mode.
After increasing my average speed from 14 mph to 16 mph after that interval training all summer, I'm plateaued again. So I've added more strength and flexibility training. Squats, legs, back and abs. Just another 5-15 minutes at home depending on time. It's helping a bit. I'm not faster yet, but my recovering time between sprints and climbs is decreasing. Instead of needing to stop and rest for a few minutes, I can just ease up a bit while pedaling and recover for another climb or sprint. That's a huge improvement over two years ago when I often needed 15 minutes to recover from asthma attacks after any high effort.