Yes. VO2 max, the most oxygen your body can use during all-out exercise, falls steadily through adulthood, and the drop speeds up as you get older. In the Baltimore Longitudinal Study of Aging, researchers retested 810 healthy adults aged 21 to 87 over a median of about eight years and found peak oxygen uptake fell about 3% to 6% per decade in people in their 20s and 30s, but more than 20% per decade in people in their 70s and beyond.
From their 40s on, men lost aerobic capacity faster than women, and the same accelerating pattern showed up at every level of self-reported physical activity. The authors also noted that cross-sectional studies, which compare different age groups at a single point in time, tend to underestimate how quickly fitness declines in later life.
Image: VO2 max treadmill test at Fort Carson, U.S. Army photo by Cpl. William Smith (public domain), via Wikimedia Commons.