representation in ms-access
The PointsForPushups table needs to be normalized first.  I suggest breaking it into the two following tables:


tblPointsForPushups
----------
reps | ageGroup | pushups
1 | A | 6
1 | B | 7
1 | C | 8
2 | A | 7
2 | B | 9
2 | C | 9
3 | A | 9
3 | B | 11
3 | C | 12

tblAgeGroups
----------
ageGroup | ageMin | ageMax
A | 17 | 21
B | 22 | 26
C | 27 | 31


With these tables in place then DateDiff and Between can easily be used in a query to find the required information.