Whilst you wait a good long time for me to get anywhere near ponytail length, here is a photo of me at about 16 taken around 1975.
It is about the longest my parents allowed it to get. I should be there again, as a landmark, in maybe 6 months. I do remember a time of being able to get the ends of my side bangs into my mouth!
Now all grey, it will look very different, but I am confident that I have almost the same volume as I had then.
Anthony
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That's a lot longer than I was allowed when I was that age!
At this age, my parent were a lot more liberal about my hair than in my "Slash Harry" days or with the barber over the newsagent's shop. I'll need to ask my father or sister for photos of me from 16 to 20 years old. I was away from home at 17, but a visit home also meant a visit to the barber for a trim!
I do remember a visit home when I was 20 with shoulder length hair. It would be wonderful if I could find a photo.
This photo of me at 16 came my way last February when my mother died, and my sisters cleared out her desk and found me some forgotten things.
Anthony
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1974 Senior Year on a visit to my sister. This is the longest my parental units allowed my hair to grow while living "under their roof". My mother cut our hair using dog clippers. They were built better than the ones made for humans, go figure.

My Parents were the same until my junior year of high school I was allowed to get it about as long as yours like in your photo, before my hair was cut like the photo below.
I'm super jealous that you guys got to be teenagers in the '70s. It seems like it was a fun time all around.
Of course, we didn't get much choice about it. I got my exposure to "modern" culture in 1971-72 and had a conventional education after that. I left school and started work in 1976 in the north of England, in a very narrow-minded and bigoted world. I spent the last 2 years of the 1970's in London with very little money.
What would I have chosen had I had a choice in the matter? The two World Wars were at awkward times, and one would have to be too young for the first and too old for the second. My grandfather was in his teens during the 1914-18 war, but was an officer in 1940 when the Germans took him prisoner at Dunkerque. Not much long hair on dudes in those days! The clippers worked overtime...
There were the 1960's when I was little. My brother was a teenager (13) in 1966 and was more influenced by it all than I was. He went up to Leeds University in 1971 and managed to get his medical degree despite all the distractions.
What would I choose? On condition of being in good health and born into an aristocratic family, perhaps the early 18th century. If you didn't have some horrible disease, you could grow your hair long - and if you were bald or had a scalp disease, you could have a powdered wig. Also, baroque music was on the Hit Parade in those days.
I think the best is what happened and the time when I did appear in this bittersweet world!
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Never thought of it that way. I guess being a 2000s teen had some advantages lol.