I know its more and more common for older couples to have kids or be the primary caregiver for their grandkids, but are they able to handle all this effort? Its an awful lot of bending, squatting and running about for people who may have had a fairly relaxing life until baby came along.

Some can and some can't. Just because they cannot run around with the child does not mean it is any less loved or has any less a quality of life.

In fact it would often seem that those in that situation are far more suited to parenthood than younger people. They are calmer, slower to anger, and generally more weathered. Less phases them.