https://www.aviationsafetymagazine.com/issues/36_6/features/Revisiting-JFK-Jr_11190-1.html
>John F. Kennedy, Jr., began his flight training in 1982. By September 1988, he had flown with six different instructors and logged 47 hours. Of those hours, 46 of them were dual instruction; one hour was solo. There were no more entries in his logbook from September 1988 until late 1997.
>Beginning in December 1997, Kennedy obtained training toward his private pilot certificate from Flight Safety International (FSI) in Vero Beach, Fla. By April 1998, he had flown about 53 additional hours, 43 of which were with an instructor aboard. According to the NTSB, the instructor who prepared Kennedy for his private checkride stated he had “very good” skills for his level of experience.
>Kennedy earned his private pilot certificate in April 1998. He did not have an instrument rating. He received a complex airplane endorsement in the accident airplane in May 1999, shortly after buying it. He held a second-class FAA medical certificate issued on December 27, 1997. It had no limitations.
Looks like he had experience throughout his adult life but only got his private pilots license in April 1998.
Can't get an exact date but I bet it is April 29th.