Do you want to achive the result in the loading script or in application level?
If you want to achive in loading script, you will need to use some aggregations with a group by clause and sone interrecord functions like peek/previous in your loading Script. Unfurtunately iam in a subway and cant test it out.
in this case a Script like this would do the trick. You now just have to make sure about your date format and your percentage Value
Load product, subproduct, type, bucket, NewMoB, min(vintage) as vintage, min(vinatgeYrMon) as vinatgeYrMon, min(NewMOBPercent) as MinValue, max(NewMOBPercent) as MaxValue, avg(NewMOBPercent) as AvgValue group by product, subproduct, type, bucket, NewMoB