A recent study asked almost 2000 women questions about their exercising, physical health, and emotional health across the years from 2001 on. All the women had at least 10 depressive symptoms at the start of the study, ranging from moderate to mild.
Across the time frame, women who did 150 minutes of moderate-intensity physical activity or 200 minutes of walking per week all improved their physical health, pain, physical functioning, vitality, and social functioning. More improvement was shown with greater amounts of exercise, but benefits were derived from low amounts as well.
The take away is that moderate-intense physical activity or walking can improve well-being, with most benefits being derived from more, but even small amounts result in improvement. So just start, even if it's a small amount there will be benefits!!