Fascinating thread.
Many years ago dsis did not apply to Oxbridge because she was a year ahead and they refused to consider an application of a 16-year-old (obviously pre-Ruth Lawrence). Bristol had no qualms about her youth (and subsequent wild ways...).
I didn't apply as I was afraid of rejection, and also - I don't know whether this still applies - other universities on the UCCA (as it was) form could see you had put Oxford/Cambridge and the received wisdom was that quite a few would take umbrage and reject you out of hand, thus potentially leaving you high and dry if Oxbridge didn't work out.
Dh's parents would not allow him to apply. What a contrast with most MNetters! Dh's headmistress actually visited their house to plead dh's case, but no, they stood firm and in fact really didn't want him to go to university at all. This was the 1980s, not the 1950s. Unbelievable.
Ds has expressed an interest in Oxford. I am walking a vaseline-smeared tightrope trying to balance encouragement in one hand and practicality in the other.