As a world expert on sore a****s (I went thro months of agony) I feel able to contribute to this.
You don't specify were/how you are sore e.g. sit bones / pedundal nerve (runs approx. from your scrotum to your bum) or chafing/soreness from rubbing.
Age IMO is also a factor as the older you get the less flexible your bones/sinews/muscles become.
If its the sit bones or the pedundal nerve...............
a) get a "bike fit" or do it your self if confident.
b) go to a decent bike shop that is able to measure you for the correct saddle..............mine turned out to be a Fizik Aliante.
c) decent shorts.............mine are Endura Pro.
I could only manage 35 miles then needed a weeks rest before getting on the bike again. After the above I immediately did a 68 miler followed 2 days later by a 24 miler...........WITH NO PAIN

.It is the difference between enduring & enjoying a bike ride............worth every penny you can afford.
Good luck with it.