If you are lucky, you will be elderly one day. If you are very lucky, you will remain independent and active as you grow older. As such, you deserve the respect and courtesy afforded the elderly in other, more age-respectful cultures. One of the primary means of demonstrating respect is the way in which we greet and speak to those we honor.
Speak clearly and use standard means of address, such as "Good Morning," "Hello" or "It's good to see you," as opposed to slang, such as "Yo" or "Heya," or the over-personal, "Pops."
Don't shout, assuming all elderly customers to be hearing-impaired.
Call a woman "Ma'am." If you know her surname, call her "Mrs. Jones" or "Ms. Smith." Do not use her first or Christian name unless you are invited to do so.
Call a man "Sir." If you know his surname, call him "Mr." Do not use his given or Christian name unless you are invited to do so.
Use "please," "thank you" and "you're welcome" to customers of any age.