There are not many adults who ride ponies aside - come to that there are not many adults who ride ponies astride!
However, ponies are quite capable of carrying adults - and this means side saddle as well!
The difficulty is getting a side saddle small enough to fit the pony but large enough to fit a lady's (ahem) rump!
I'm not that large in that area though - and although I say so myself, I think I look quite good aside on my Exmoor Pony.
(note: I have the wrong coloured gloves, the apron needs an iron & I need to get keepers on the girth straps)