This one does not. 1 in standard units. You would be too low, because the curve is lower than the histogram in that range. The data are cross sectional, not longitudinal. In the early part of the century, there was much more pressure to conform and be right-handed.
Age is a risk factor for heart disease, hence a potentially confounding variable.
First, it seems plausible that drivers and conductors are drawn from similar segments of society. The executive staff is likely to be better educated and more affluent, hence have different lifestyles that would confound comparison. Second, drivers and conductors are subject to nearly identical working conditions, whereas the executive staff work in offices. Again, the goal is to find groups that differ as little as possible except with respect to the variable of interest. This was an observational study, so the possibility of confounding variables was considerable.