Fun read, Olive Green! Thank you!
I've been high image interest for most of my life (from childhood, really) with a dip to low in my late 30s to late 40s for reasons having to do with low income, jobs that demanded the most practical clothing possible, and then some weight gain and childcare.
I'm not particularly interested in makeup or beauty products or hair (apart from picking a style I like that suits me). It's the fashion part of it that interests me. I also have a high interest in home decor, art, architecture and design.
I do find that big life changes (jobs, moves, etc.) can occasion a kind of wobble, as Brooklyn indicates. It can take time for me to figure out how to adapt to a new situation in a way that combines my practicality with my high image interest. Both are very strong in me, so it can be a bit of a conflict!
My mum's pattern was very similar to my own -- high interest up until her mid-to late 30s, I'd say -- then a period until she was around 50 where it was low, and then it increased again. She couldn't shop by then but loved the fashion pages and enjoyed getting dressed up to go out.