I am in my 40s and in California shape from walking around Santa Monica with Sweet-Boy Toby, my 9-year old Chow-Shepherd mix. Because of all the walking we do, Toby looks like he is about 5-6 years old. Toby is sweet and gets along well with all the dogs we watch at my apartment. I generally take only one other dog--so it is two at any one time, including Toby. Toby and I go for a one-and-a-half hour walk every morning, down shady Santa Monica streets, north of Washington and south of Georgina. I bring water, but occasionally will let Toby drink out of select Montana water bowls--only a few meet my standards and Toby has never gotten sick. Very often, with stops at Starbucks, this walk turns into 2 to 3 hour outdoor time. In the early afternoon, Tony, my tenant and good friend, walks Toby for another hour. I then walk Toby in the evening between 9 and 10 for about 10-15 minutes so he can pee out before bed. These times can be adjusted to accommodate your dog, but I promise, the lack of a yard will be completely made up for with walking and just being outside. Plenty of exercise/plenty of stops and water when needed. I also adjust my day care and dog walking rates downward for long-duration requests - just ask!