My DM is a serious hoarder. She still has all my old school books and I am 48 this year. My sister is just like her and has a tiny house filled to the brim with clutter and crap she doesn't need.
I am the complete opposite and regularly have spring cleans. For example, every 6 months I go through my wardrobes and ask myself 'have I worn this in the last 12 months?' If the answer is no, it goes to the charity shop. When my DS grows out of stuff, I pass it on to other family who have younger boys.
I keep one folder, with special school things for DS - school report or a nice picture or story. Everything else from school gets binned.
College and Uni stuff have been binned/recycled.
Wedding dress got sold 2 days after I got back from honeymoon.
DS's first pram got sold as soon as he no longer used it.
I have nothing in my loft or my garage.
I think sometimes you either have to make a choice to just be ruthless and get rid or try to identify why you feel the need to keep things. My Mum is a hoarder due to her mental health. My DSis is a hoarder because she doesn't earn a lot of money and feels the need to have 'stuff'.
I just can't be doing with clutter - just the way I am, as I like control and order. Good job my son is the same or he would get pretty upset at me not keeping all his school stuff.