The author (left) is older than his partner (right).

Courtesy of Bil Browning

I'm 53, and my partner is 29. When I moved to Mexico City and we started dating, I posted a photo of us to Instagram, and my American friends lost their minds.The daddy references started immediately. When one person asked if I was a sugar daddy, I pointed out that Uriel makes more money than I do. I'm Splenda at best.I was self-conscious at first, but the insecurity faded when it became obvious the age gap wasn't a big deal in Mexico. Eventually, we were just a couple who shared common interests and a crusty little white dog, Maggie.Until recently, that is.I tripped and hurt my kneeMaggie lived on the streets until she moved in with us. She still has the annoying habit of gulping down anything that remotely looks like food she finds on the sidewalk, and sometimes it doesn't agree with her. About a month ago, one pavement goodie led to a trip to a veterinarian.We circled among three clinics in our neighborhood, looking for a vet who was actually available; either he wasn't there, or the office was closed. Defeated, we decided to head home and try again the next day. That's when it happened.I tripped on the sidewalk, and while I stayed upright, I landed hard on my right leg. At first, I seemed OK, but within a couple of blocks, my knee let me know that something was decidedly wrong. By the time I limped in our front door, I could barely walk.After spending two days in bed with an ice pack and Advil with little improvement, I knew it was time to see a doctor. After examining the X-rays, he gave me the worst possible news."You're getting older," he started, and I immediately knew this wasn't going to end well. "You have arthritis in both of your knees, but it's much worse in your right."