You can't use the class function since you have unequal class sizes. Applymap also doesn't have anything to offer afaict. What you can do is move the amount check out of the nested if so you only check the ages in the nested ifs construction. That should simplify things.
IF AMOUNT<0, 'DR ', 'CR ') & IF( ...nested age checks here... )
Also, this part doesn't make sense:
IF( Age >30 and Age <=60 and AMOUNT<0,' DR >30 Days',
IF( Age >30 and Age <=60 and AMOUNT>0,' CR >30 Days',
IF( Age >=30 and Age <=60 and AMOUNT<0,' DR 30-60 Days',
IF( Age >=30 and Age <=60 and AMOUNT>0,' CR 30-60 Days',
The two last ifs will only match if the age is exactly 30. Any other ages between 30 and 60 will be shown as >30 Days.