We just saw this show in Australia today. I thought Dr Phil was too hard-line with Shelly and Mark. It's not as if this age difference could NEVER work, just that it's less likely with him being so young. He's also assuming that every relationship has to be entered with the plan to make it "happy ever after" whereas I feel there's value in short term learning and growing experiences as long as everyone involved is on the same page about what it is. Here in Australia Mark would be considered an adult and equally responsible for the relationship and his choices.
When I was 36 I had a wonderful short-term relationship with a 23 year old, it was incredibly restorative to me having come out of a marriage in which I wasn't sexually appreciated. He didn't suffer too much from it ... other than exhaustion sometimes! In this case, he decided we didn't have enough in common to take the relationship further and he was probably right in this (he was a champion hockey player and I'm not THAT active!). However, we stayed friends a long time after, even when I remarried (someone my own age with whom I broke up 11 years later! Just not enough in common there).
I am now happily with someone 15 years my junior (he is now 37 and I am 52), we have lived together for 4 years. Does it make all the difference that he was 33 when we met? Definitely old enough to know his own mind and to know I was who he wanted to spend his life with. I have never wanted children and took steps at 28 to make that an impossibility, so perhaps that's why I'm not squicked out by the "I could have given birth to him" thing as some women seem to be. Having been with other older women who had kids, he'd already made the decision they were not for him! I am not mutton dressed as lamb, but I also don't look my age, so very few people give us a second look as we get around the small town we have chosen to live in. We have so much in common, we play heavy rock music together in a band, like similar books, movies, TV shows etc. His family has accepted me totally as they are just so happy to see him happy, likewise, my Mum thanks him for giving her "my daughter back, she was so snappy when she was unhappy". We are looking forward to growing old disgracefully together!
As a professional, I think Dr Phil should try to step outside of his own values and prejudices sometimes and look a bit more objectively at a situation.