Ah yes,
Those tough dilemmas in life ...
In any case, my advice is to keep the Corsa if only because of that ridiculous insurance premium. It does not make sense! As for the young driver issues. Well, I am no expert here but being 23 (got the license at 18) I would say that I can understand what the 'old' lads here are pointing. Also, please be aware that sl500 IS fast and powerful and 440 bhp is not at all for the faint of heart. Hell, your Corsa is fast too if you compare with a bicycle. You see my point?
Anyway, far be it from me to tell you what to do and I am sure you are a skilled driver but you have plenty of time to play and pay with a 440 bhp super car.
This forum by the way is an amazing (non)-reality bubble ... I mean; anything with under 300 bhp is considered a slouch and 21 year olds are cruising around in B7 RS4 ... can I have some of that Kool Aid please?