How old must you be to be considered a "senior citizen?"?

[Healthy Environment]

Is there an official senior citizen age? a lot of senior discounts are given to people at 55+. Does that make 55 the official senior citizen age?

AARP let's people join if they are 50+.
To withdrawl social security, you must be at least 62.....62 is considered early, 65 is considered on time.

Is there an official senior age, or does the term "senior citizen" simply mean "old person" ?
OK people, 40 is not old. 40 is middle-aged.

18-39=young adult
40-59=middle-aged
60+=old

I dunno what you would consider a senior citizen......but 40 is not considered old. It's becoming increasingly common for people living to 100+.