I'm 48 and have 12. I also have 3 denim waistcoats.
Most are years old but all get a wear latebspring to early autumn. Although they vary in could and style I see them as a classic wardrobe item that can go with most things. I choose a denim.jacket over a cardigan alot of the time.
French Connection indigo blue fitted
Monsoon mid blue classic
Joules off white
River Island light blue cropped
Red Herring v pale pink
John Lewis Blue Blazer style
Oasis khaki
Next Black
Karen Millen indigo blue slightly cropped
Monsoon White cropped
Oasis Pale yellow
Calvin Klein light blue
I've got my eye on a nice Ted Baker one at the moment too.