In 1955, ten year old Jayne Ann Henly completed a day hike to the summit of Mt. Whitney. It was a record at the time.
Today, Dr. Jayne Ann Henly Antony is a pediatric Neurologist in Sydney, Australia.
Here is her picture at the Mt Whitney summit, July 28, 1955.

In preparation for the hike, Jayne and her father and uncle climbed Telescope Peak three days earlier, on July 25, 1955.
Here is a picture taken from the top of Telescope Peak:

And here is Dr. Jayne Antony in a recent picture (front row, center) with her paediatric neurology colleagues working with her at the Children's Hospital Westmead (Royal Alexandra Hospital for Children) in Sydney.
(click on each picture to see the full size image)
Here is the text from several emails Dr. Antony sent me to report her historic accomplishment:
Aug. 7, 2010
My name is Jayne Antony and I am a paediatric Neurologist in Sydney Australia where I immigrated in 1974. I was born and raised in the USA and in July 1955 I, with my father Wayne Henly and Uncle Stanley Howell climbed to the peak of Mt Whitney in one day and signed the book (as Jayne Henly). I was born on the 9th January 1945 and, thus, was 10 years old. I have looked at websites and it appears that children older than I was at the time have claimed to be the youngest to climb the Mountain. I have photos and newspaper clippings and wonder if you could guide me as to who I should send them to (once I dig them out of storage!!)
Sincerely,
Dr Jayne H. Antony
Aug. 8, 2010
My Uncle Stan was a physicist for NASA at China Lake Ca. We lived in Jacksonville, Illinois, and used to visit him every summer. He died a few years ago but my father is still alive. My mother tells me that there was a letter to the editor in the Saturday Evening Post sometime after my climb but I am not sure what edition but I may have it somewhere. You might ask why I have explored this now after so many years (in fact decades)...the answer is that I have a phobia about heights particularly sheer drops and I have always (rightly or wrongly) explained it by my experience on the switchbacks from my hike in 1955. I was talking to a colleague about this and it entered my mind to find out what is on the internet about Mt Whitney. A bit of a buzz to speak with you and bring back all of these memories. I look forward to getting all this together and sending it to you...must be old age that I am getting nostalgic!!
Best regards, Jayne
Here's the clipping from the Saturday Evening Post, June 16, 1956:

Aug. 9, 2010
I cannot imagine that your friend has not heard of my Uncle. I think he was very well known. He died several years ago and I think he was born about 1920 since he was a couple of years older than my mother born in 1922 (and still alive). I am delighted to tell you that I have actually found all of the newspaper clippings, photos of myself on top and even the letter to the editor from the Saturday Evening Post. I will get my secretaries to scan all of them and email you. Even though you are probably correct about the cause of my fear of heights being in my genetic makeup, it did motivate me to look into to this and find out that no one knew of my feat. Incidentally, the actual day was Thursday 28th of July 1955. Do you still have the pages from the visitor's book relating to that. Thanks..
Jayne
Memories of the hikeAug. 13, 2010
My memories are very sketchy after half a century. I recall that the Telescope Peak hike was relatively short and my 8 year old sister sat down about half way and waited for us to go to the peak and come back...somewhere we had a picture of her sitting there with a squirrel nearby (is that possible). All of the photos were 35mm slides and the only ones my parents sent to me were the two you have which they made into prints since I think the slides were fast fading. They are still around living in Columbus, Georgia, and are on line if you have any questions of my father, Wayne.
Regarding the Mt Whitney climb...I certainly recall starting in the dark with flashlights. The trail was rocky but well defined and the switchbacks are still in my memory and I was always relieved when we were on the other side. I sort of remember that the very last part of the climb was the most rugged and tricky but it never crossed my mind not to go on. I certainly remember the top, the cabin and signing the book, AND having that photo taken.
The descent I think was uneventful and sometime I bought a salt and pepper shaker from a shop in Lone Pine!! Isn't the Brain weird and wonderful with what it stores....probably why I am a Child Neurologist. This was the dark ages without mobile phones so that my last memory was my Aunt Iris (Uncle Stan's wife) standing in the doorway when we drove back to the house in China Lake saying "did you do it" and my Uncle's reply...."we sure did !!"
From what you say below (regarding the altitude) my Uncle must have known what he was doing by having me climb Telescope Peak first. He climbed a lot in his time in California, my father was a letter carrier in those days and walked miles everyday. As for me I was a bit of a "tomboy" and physically very active and fit but, of course, there were not a lot of mountains to practice climbing in Jacksonville, IL!!. Don't know why I didn't have any altitude problems but, if I was uncomfortable, I have suppressed that memory! Don't think I can recall anything else but if you have any questions it may jog my memory.
Best regards, Jayne
Picture source is here.