Parameters do not work that way. They take on only a single value, although it can be limited to a range.
This is a calculated field that will assign a generation to an individual based on their birth year.
If Year([Birth Date]) < 1946 Then 'Veteran'
ElseIf Year([Birth Date]) < 1965 Then 'Baby Boomer'
ElseIf Year([Birth Date]) < 1977 Then 'Gen X'
ElseIf Year([Birth Date]) < 1995 Then 'Gen Y'
It can now be used to group records.
If you wanted to be able to change the range for the generations, then you could create parameters for each of the hard-coded years, however, it would be possible for them to take overlapping values -- i.e. each parameter is separate.
Hope this helps.
Thanks Brian! It's working now.