I've got some stuff in my wardrobe that is probably 20 years old, it doesn't fit (at the moment as I've put on weight) but it's things like favourite t-shirts.
Generally I throw clothes out when either they don't fit, or are worn/damaged and have no further use (I keep old jeans/t-shirts and tops for things like painting/gardening where they're likely to get knackered fast).
i loathe clothes shopping, especially as it always seems no two stores quite stick to the same sizing and some stores don't even stick to the same sizing within their own range. The only thing I find worse than clothes shopping is shoe shopping because none of the highstreet stores actually seems to carry size 12's, let alone 12 wide or 13's most of the time*. it seems that every time I go to buy some I end up half killing myself going around all the shoe sellers in the surrounding towns, then having to order the ones I liked the look of from their online store as they didn't have anything over a size 10 in stock, only to find it doesn't fit.
On a tangentially related note, I was popping out to do some bits in the garden and realised my mobile was low on charge, no problem I thought, I've got powerbank and I saw a my old bumbag in the bottom of a drawer with some old console bits.
I was oddly saddened to realise the bum bag that always seemed to be loose when I wore it, doesn't actually fit me nearly 30 years later.
*With Clarks I'm usually a 12 wide, or 13, but can squeeze into a 12 depending on type of shoe and style.