40! But actually that didn't surprise me as I've always been aware of this ability to visualise things, people etc. My sister and I used to share a bedroom and would lie in bed at night describing to each other the vivid scenes that randomly unfolded in our heads. There would be people involved in various activities and I would be able to see their faces as clearly as if they were in the room with me, people who, to my knowledge, I'd never met (though of course they may have been in my subconscious from having seen them in the street or on TV etc.). I could describe the surrounding countryside down to the buttercups growing in the fields. My brother never really got this and always maintained it was imagination. It wasn't, because these were scenes I could see, like a film running through my head. I didn't know what was coming next, I wasn't consciously 'making it up'.
Sometimes we would suggest a scene to each other, and it would appear in my mind's eye, just like that. It might be an urban landscape, for example, and I would be able to describe in detail all the shops I was walking past, the colours of the doors, etc. etc.