soft question - Mathematicians who were late learners?-list

In May 2006, the AMS Notices printed a remembrance article for Serge Lang. Dorian Goldfield was one of the contributors, and as an undergraduate, he described himself as follows:

Of the many people who had serious
interactions with Serge, I am one of
those who came away with fierce
admiration and loyalty. In the
mid-1960s, I was an undergraduate in
the Columbia engineering school on
academic probation with a C–average.
In my senior year I had an idea for a
theorem which combined ergodic theory
and number theory in a new way, and I
approached Serge and showed him what I
was doing. Although I was only a
C–level student in his undergraduate
analysis class he took an immediate
interest in my work and asked Lorch if
he thought there was anything in it.
When Lorch came back with a positive
response, Lang immediately invited me
to join the graduate program at
Columbia the next year, September
1967.

Then again, Goldfield was not a "late learner" as he was 20 when he finished college and 22 when he earned his PhD. But...