Channing Muller had always dated men close to her age — usually a few years older, in fact. But after a horrible breakup in 2019, she decided she needed to try something new. Her therapist had an idea, suggesting she look at guys outside her usual range.  “He was, like, ‘Go 10 years up and 10 years down and just see,’” Muller, who runs her own communications firm in Chicago, recalled to The Post. So Muller, then 34, went on the dating app Bumble and changed her age preferences. She was