Are there any famous pianists that have only started piano in their adolescent years?
I’m afraid not. “Developing Talent in Young People” by Dr. Benjamin Bloom has a chapter devoted to concert pianists. One of the author’s grad students sent out a questionnaire to concert pianists, asking about their earliest musical experience. The respondents tended to reply that they started at a young age with a woman who was good with kids but did not necessarily have lofty musical qualifications. When the student got as far as he or she could with that teacher, the student switched to another teacher who had lofty musical qualifications but was not necessarily good with kids. By that time, the student’s motivation was well enough established to insure that the student would continue studying if the teacher threw a Toscanini tantrum.