One parent over 60, and second time visa application...

Hi,

We're planning to get my parents-in-law over from India. Had a few questions in this regard:

1. If only one of them is over 60, are both eligible for a drop box? If not, can my FIL request for a consular interview inspite of qualifying for the drop box?
2. Assuming they get their visa for 6 months, visit us and then return to India, is there a time limit before which they can apply for the visa again? Have visas been rejected the second time, because they were applied immediately?

thx,
Chand

only the one who's age is => 60 is qualified for the DropBox. The person can still avail Interview by setting up an appointment. If they want to go together setup interview for both.
there is no limit they can apply any time.