If you want to use IF Formula, its nested Ifs & array formula.
Assuming that the data is in D2 & you want the ageing (result) in E2, The data Ageing & Slabs data are in A & B.
=IF(D2=$A$2,$B$2,IF(D2=$A$3,$B$3,IF(D2=$A$4,$B$4,IF(D2=$A$5,$B$5))))
(Shift+Ctrl+Enter) Array Formula