Johnnie and math Ph.D. here. It's a bad, or at least slow, way to prepare for math or math-heavy graduate school as you'll need to take additional coursework elsewhere in order to be competitive. On the other hand, freshman math at St. John's (Euclid, a bit Apollonius, start into Ptolemy) was for a significant fraction of students in my year the first math class they had ever enjoyed. Euclid's Elements, despite its many inefficiencies, and faults, does not heavily rely on mastery and/or acceptance of earlier curricular material, nor is it designed in service to later curricular material that most students are in no position to anticipate or appreciate.
On the third hand, reading Newton is a really bad way to learn calculus; the college uses a lab manual which more closely resembles a modern calculus course.
On the third hand, reading Newton is a really bad way to learn calculus; the college uses a lab manual which more closely resembles a modern calculus course.