An April 2021 study by Purdue University said, 

"In our study, we focused on couples because partners in committed relationships often provide essential support to promote one another's healthy lifestyle behaviors, including exercise," 

"We were hoping that there would not be a reduction in speed where partners walked together. We hoped that slower partners would speed up to match the faster partner, but that was not the case. However, it's important to note that any physical activity or walking - regardless of speed - is better than none."

"If someone substantially slows down when they are walking with someone else, that could negate some of the health benefits recognized if they walked alone at a faster pace,”

"Gait speed is important to measure because it is related to overall health. Typical gait speed is predictive of fall risk, functional ability, disability recovery and mortality,”

"Common exercise interventions, including strength, coordination and multimodal training, are all effective in increasing gait speed. These interventions can also delay the onset of slower gait speed and help slow the loss of gait speed. No one type of training is better than the other, so do the activity you are most likely to stick with."

"Older adults who are more active tend to maintain their gait speed," 

"In other words, slower gait speed is not an inevitable aspect of ageing. Older adults who walk slower tend to have poorer health and lower functional status."