Determine whether a set of age labels refer to one-year, five-year, or life-table age groups.

## Details

The valid types of age labels are:

`"single"`

. One-year age groups, eg`"0"`

or`"55"`

, and possibly an open age group, eg`"90+"`

.`"five"`

. Five-year age groups, eg`"0-4"`

or`"55-59"`

, and possibly an open age group, eg`"100+"`

.`"lt"`

. Life table age groups, eg`"0"`

,`"1-4"`

,`"5-9"`

,`"55-59"`

, or`"80+"`

.

If `x`

does not fit any of these
descriptions, `then age_group_type()`

throws
an error.

If `x`

could belong to
more than one type, then `age_group_type()`

prefers `"single"`

to `"five"`

and `"lt"`

,
and prefers `"five"`

to `"lt"`

.