Thank you for the reply, ajb.
A PhD would be nice, of course, but first I'd like to study on my own and see where that takes me.
I recently bought the following books:
"The Math Book" (cover says: from pythagoras to the 57th dimension, 250 milestones in the history of mathematics) by Cliford A. Pickover
"Mathematics 1001" (cover says: absolutely everything that matters in mathematics in 1001 bite-sized explanations) by Dr. Richard Elwes
These were found from a while back:
"Mathematics: From the Birth of Numbers" by Jan Gullberg
"Advanced Calculus" (second edition) by Robert C. Wrede and Murray Spiegel
After the Holidays (Happy Holidays, by the way) I plan to study those books, day and night, until I learn it all. Until I get that sense of mastery. Until every thought and every dream is about math in some way. This may take a very long time, but I'm willing to put in the effort.
Good luck to you, too.