I didn't think of Lazy town at all when i 'heard' the name. It put me in mind of a lovely girl that i went to school with (and i'm not middle aged ...yet )
Yes, i think its a grown-up name - but how can that be a bad thing? There are some lovely diminutives for Stephanie (Stephie, Stevie etc) so would work well for a baby and a grown up, IMO.