"Regular Occupants"

I'd consider employees (full and part-time), residents, and students (4th grade and higher) to be defined as "regular occupants" for the purposes of this credit. I would define retail-type customers (e.g. bank, grocery store, health club, etc.) to be visitors.

I am not aware of an upper age limit (similar to the lower age limit) that excludes people from the credit's occupant count.  

The Reference Guide Overview provides a description for regular occupants.

"Regular building occupants are habitual users of a building. All of the following are considered regular building occupants.

Staff is synonymous with employees for the purpose of LEED calculations.

Volunteers who regularly use a building are synonymous with employees for the purpose of LEED calculations.

Residents of a project are considered regular building occupants. This includes residents of a dormitory. If actual resident count is not known, use a default equal to the number of bedrooms in the dwelling unit plus one, multiplied by the number of such dwelling units.

Primary and secondary school students are typically regular building occupants (see the exception in LT Credit Bicycle Facilities).

Hotel guests are typically considered regular building occupants, with some credit-specific exceptions. Calculate the number of overnight hotel guests based on the number and size of units in the project. Assume 1.5 occupants per guest room and multiply the resulting total by 60% (average hotel occupancy). Alternatively, the number of hotel guest occupants may be derived from actual or historical occupancy.

Inpatients are medical, surgical, maternity, specialty, and intensive-care unit patients whose length of stay exceeds 23 hours. Peak inpatients are the highest number of inpatients at a given point in a typical 24-hour period."