We applied to at least 20 sits before landing one! We eventually got lucky. Our first host was a young person, in his late 20’s. His parents told him to “look for a retired couple” to sit for your dog (in San Francisco, very nice location).
We happened to fit the bill!
There is some great advice in this thread:
The perfect application?
Focus on how you can fulfill the actual needs of the host, rather than on how you are great at photography, and that you want to travel.