Seriously though it's going to be difficult to get a one size fits all...
My girlfriend is tiny and she can just about ride my 56 with the saddle fully down... I'd recommend getting a 54 and make sure you've got a long seatpost for adjustment but also shorter cranks for little folk... Add to that a short enough stem with bullhorns or a longer stem with sweep back bars (something with a number of positions lenghtways) . Then you need a saddle that caters for men + women and various sizes... probably a Concor...
If they want it to be trendy I'd recommend a coaster brake singlespeed hub somewhere around the 70-75 GI ratio... it'll look tidy...
Ideally your best bet would be to go for something like this:
How about something like this??
Seriously though it's going to be difficult to get a one size fits all...
My girlfriend is tiny and she can just about ride my 56 with the saddle fully down... I'd recommend getting a 54 and make sure you've got a long seatpost for adjustment but also shorter cranks for little folk... Add to that a short enough stem with bullhorns or a longer stem with sweep back bars (something with a number of positions lenghtways) . Then you need a saddle that caters for men + women and various sizes... probably a Concor...
If they want it to be trendy I'd recommend a coaster brake singlespeed hub somewhere around the 70-75 GI ratio... it'll look tidy...
Ideally your best bet would be to go for something like this:
OR
The first is much nicer though...