Tony Horton, best known for the P90X workout, says he's thriving at 66 after tweaking his routine. Horton was diagnosed with a rare illness in 2017 and has since followed a flexible plant-based diet.

DALLAS - Tony Horton - effusive, energetic, enthusiastic - bounds into a hotel ballroom on a recent Saturday morning and leaps onto the platform set up for him. The 300-plus people in the crowd cheer ...