This is something that I've seen vary dramatically from person to person. Some people began to stop playing with toys at around nine, others eleven, some I've even heard have gone into their twenties before fully ceasing. For me, I think the last time I actually "played" with toys was around age twelve, which, as far as I've understood, is one of the later ages.
Expression of imaginative ideas was something that I didn't find possibly through any other form but usage of toys. They were, in reality, a conduit that I projected adventurous concepts I could never actually perform. Because of that, I never really felt myself desiring to stop until I was older than a lot of kids.
So how about the rest of you?
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Probably around 12, I use to love playing with hot wheels.