Retirement tax questions

They ask...what is the earliest age you could have retired if you hadn't retired on a disability?  Why do they care and There are a couple different options for retirement and I don't know the correct answer.  For instance, you can retire at 55 if you have enough years of service  that when added to 55 ='s 83 or 85 (I forget which). etc.  soI arbitrarily put 65.  Does that affect my taxes?