riding a geared 50cc at 16 isn't illegal as long as you pass your cbt on a geared bike, when you do your cbt you will be asked if you want a geared bike or a automatic, i would go for geared anyway that wat when you turn 17 you can just get a geared 125. theres a range of geared 50cc bikes about now just steer clear of chinese bikes that have been abused, im not saying dont buy a chinese bike despite what people may think some of them are good bikes i have had a few and if looked after, same as any other bike in all honesty they will see you right.
parts are available easily aswell with most chinese bikes been based loosely on honda's mostly so parts are easy to get hold of, as for the fs1e mentioned before that would be a great bike for what he wants but trying to find one that dont need restoring could cost a pretty penny, but there again you could tell your mum and dad you really need the bike and with all stress of divorce etc. it would make you feel much better if you had one lol
good luck in your quest mate just remember 1 thing BE SAFE!!!!