In my mid-30s and have noticed the older i get, the less my digestive system is able to tolerate certain foods that i used to eat easily. why is that?

Gut Sensitivity: This has nothing to do with getting older per se but has to do with the damage in your gut that has occured from consuming processed foods which our stomach and bodies can't digest too well. The closer to nature the food the better for your overall health, especially gut health. Start a good quality probiotic and see the intolerance start dissappearing.