I normally would not recommend growing in to a board. My motto is “I wouldn't plan on 'growing in to' a snowboard size unless you plan on 'growing in to' a good time.”But in your case, you really are stuck between Kids' and Men's sizing, so I would have to recommend going with the small Men's boards. Yeah, you probably could ride a 24.3 cm waist width board like the Radium, but I wouldn't go any wider.
