Sol's realised that Conan's young because of his voice and attitude, but since he's blind he can't see Conan's body anyway; so I think it'd be pretty easy to avoid him figuring out there's something off there!
On seeing his soul Sol will probably assume that Conan is much older than he sounds (even older than he actually is), but because Sol is used to people's appearance not matching their age (Sol himself looks in his 30s, but he's over 400), I don't think he'd think of Conan's situation as being weird enough to wonder about. Probably be amused/impressed that Conan is capitalising on his voice/looks, though. :P
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On seeing his soul Sol will probably assume that Conan is much older than he sounds (even older than he actually is), but because Sol is used to people's appearance not matching their age (Sol himself looks in his 30s, but he's over 400), I don't think he'd think of Conan's situation as being weird enough to wonder about. Probably be amused/impressed that Conan is capitalising on his voice/looks, though. :P
Does that work for you?