My friends who are psychiatrists rarely seem to retire. As they get into their 70's, they often scale back and see fewer patients, but they often continue to do administration, writing, teaching, etc. From what I can tell, the underlying motivation stems from the fact that they love their work and enjoy keeping sharp.
This reminds me of articles that I've seen that find that psychiatry residents are stressed. One of the reasons for this stress is psychiatry's underlying complexity, but it is likely that this same complexity helps make psychiatry a lifetime vocation and avocation for many of us.
Psych is not such a field for some, however, particularly those who get burned out, bored, corrupted, etc. That is why--from my perspective--it is useful to hang around people whose enthusiasm and curiousity are likely to make your days interesting, which is why it might be important to jump into the field with both feet (ie work hard) rather than treat it as a 9-5 job (especially during your training).
