Only 15-and-a-half more years 'til the 2032 Olympics ... and Michael Phelps is wasting no time getting his 6-month-old son, Boomer, ready for action!
The Olympic hero took his kid to his old training pool in Baltimore -- where Boom got a lesson from dad's very first swim coach, Cathy Bennett.
Mike's wife, Nicole Johnson, was also there.
So, how'd Boomer do?
Actually, not bad for a baby ...