Our oldest Med/Surg nurse is in her mid to late 50's, and we have a range of ages working on our M/S units. I would only suggest that a person be in fairly decent physical shape as the work can be so physically demanding and there never seems to be enough help. There are nights I call it "aerobic nursing" as I seem to run most of my shift! Of course, keeping your back strong is important, too. I'm 47 and have been working Med/Surg for almost 10 years, and hope to keep going at least another 10 if my body holds up. (Due to the stress and increased patient acuity and nurse : patient ratios, I think my MIND is likely to go first! :stone) I try to work out regularly and include cardiovascular, weights, and stretching to keep up with the demands of nursing-- and an aging body!
Mentally and emotionally, being older could mean a person has more patience, empathy, and maturity to offer, but there's a need for great flexibility, quick-thinking, organizational, and coping skills for all that Med/Surg entails. (I know because I have to keep working on these areas myself!