It's difficult to say for sure from such a general description, but usually such a system would look up a value from one or more related tables in order to either display or compute the desired result. Such a table can be set up so that a range of different values in the main table match to a single value in the look up table.
As is usually the case, I think you have got it figured out. Can you give me some direction on setting up the calculations such that a range of values correlate to a single value?
Here is a link to a similar web based calculator if that helps to clarify the intended goal.
No calculations are needed, you can specify it in the relationship to the look up table by using multiple match fields and inequality operators.
MainTable::Age > LookUpTable::MinAge AND
MainTable::Age < LookUpTable::MaxAge
And in some cases, you may be able to sort your relationship and then only use one pair of match fields with an inequality operator.