Why should I...?

Hello, everyone.

I am a bit upset, right now. Not with anyone on the 'net'. I have been watching and listening to the people in my part of the U.S. and I am not liking what I see and hear.
I have been noticing the way that many Americans (especially young people) expect people my age to do and to be. Let me explain. When I get out and do my walking for exercise, I wear earphones and listen to fast-paced music on my MP3 player, and I walk fast to the beat of that music. As I walk, I have noticed how a lot of people stare at me, or whisper to one another as they watch me walking by. Some of them even laugh aloud.
I don't think that is right. I am not like a lot of individuals my age. It is true I have many aches, pains, and ailments, but I just don't let them stop me, or even hold me back, like some older people.
They call us Senior Citizens if we're over fifty, which doesn't bother me, as long as they don't expect me to act like an S.C.; Not Happening! I tell everyone that they can say I'm old when I say I am, but not until then. And they can box me in when I am ready to be buried, but not until then. I'm talking about the kind of boxes which have labels on them; stereotypical ones. Just because an individual is older that doesn't mean he or she is ready for a wheelchair or even a cane.
I can still walk about 6 kph (3.4 miles an hour), which is pretty fast for an 'old' lady! My 24-year-old daughter is a snail compared to me! A few years ago I even took a hike up to the top of a nearby mountain peak. (More than 160 meters high, and I never even had to stop to catch my breath!)
I don't understand why 'Seniors' are put into certain categories. If I can walk two blocks to the grocers in 5-8 minutes, what's wrong with that? If I were still 20-years-old, no one would give me a second glance. But because my hair is no longer brown, I get stares; even from some people my age and older.
Where is it written that I and others like me are supposed to 'creak' and 'creep' around as though we have rusty joints? Not in my book! This 'old' lady is not going to 'act her age' as the saying goes; not when it comes to behaving like a Senior Citizen. No one on Earth can show me where it is written in any book, or any law, anywhere, that says I, and others like me, can't act younger than our years! And that is exactly what I am doing and will continue to do, as long as I am able to do so. If God is willing, and I have my way, that will be for the rest of my life. I am not alone in my thinking, either. I have an older gentleman friend who is 72-years-old and walks over 6k (3 miles) every day. (Way to go, Dwight!) And, there are many many others out there, too. (More power to them, as well!)
Thoreau wrote of the "Different Drummer" hearer: "let him step to the music which he hears; however measured or far away". I adhere strongly to that philosophy. I believe human beings were not meant to 'age gracefully' when it comes to being less active. I think we are supposed to stay active in order to stay healthier. I am giving it my best shot. For those 'seniors' out there who happen to read this, maybe it will encourage them to seek a less aged outlook and lifestyle. I hope so. I always wanted to start a revolution; at least on a small scale. Perhaps, this is my chance. Thank you.
Anna