I started noticing in my early 20’s that I would very quickly forget things I no longer had a reason to remember. Phone numbers, part numbers, general info no longer pertinent etc. Prior to that I seemed to remember everything and those things continued to stay in my memory for decades. As adults do we use a different method for memorizing things and store it differently somehow?
I worked as a truck mechanic all my adult life. I would remember every trucks mileage, serial numbers, engine and chassis specs etc. Once we were staffed with computers containing all this info I no longer remembered even the most basic specs on the trucks. I don't believe this happens consciously.