You shall honor an elderly person, and you shall fear your God, for I am God (Leviticus 19:32).
This mitzvah is of particular importance in our times, when many people are living to an older age.
Living longer does not always bring the joys of the golden years that some people expect. The "fifty-two weeks of vacation a year" after retirement are often not a blessing; finding themselves with much time on their hands, many retired people are extremely bored.
Not all couples age together; as our life spans increase, so does the possibility of losing our partner and remaining alone for many years. Children may live far away, and even when close, they may lead busy lives with little time to devote to their aging parents. The wear and tear diseases - emphysema, arthritis, osteoporosis - may make many people housebound. Failing sight and hearing make the radio and television useless companions. While we pray for long life, the "golden years" may be very, very lonely.
In a society which prizes productivity, the elderly do not have much value, and although society may pay its debt to them (albeit in inadequate payments), it may be done with an attitude that is characteristic of a debtor to a creditor: resentment.
As is evident in the construction of the verse cited above, the Torah equates honoring the elderly with honoring God Himself.