Maybe include altitude in both metres and feet, otherwise 80% of comments will be about that whole discussion.
I went up my Warning in NSW Australia, it's about 1900m. I know it's not that high but it's hard to find people who want to go on long hikes.
About 30-40 meters. Not sure exactly. It was a hard climb without a path. Just rocks and bushes. Quite steep too. But the view was terrifying.
The highest mountain I ever climbed was the two meter hill near my old home. I had to climb it whenever going to and from school. You could sometimes find me chilling half-way up the trek.
Were you always able to do it without oxygen masks? Maybe you can do the sequel to 16 peaks on netflix! ;)
All the way from bottom to top while hiking, the highest was probably Old Rag Mountain in Virginia. About 900 meters (2952 feet) at the top. Trail is moderate incline with a little rock scrambling at the top. Big boulders at the top to lounge on and great views. It used to be fairly obscure and you wouldn't see many people but now it became popular with the Northern VA/DC/MD crowd and it got so crowded you have to pay a fee and I believe make a reservation to climb it now.
I have also climbed straight up a wild mountain with no trails in Grant County, West Virginia. It's about 700 meters (2296 feet.) We crossed a river and went straight up, using trees to pull ourselves up the steep slope for most of the way. I'm not sure what the mountain is called, but it is rocky at the top and has a great view of a campground below.
I was a teenager, cannot remember any numbers but I do remember the sound of wind was very particular. It almost sounded like we could hear planes passing by.
Don't remember the elevation, maybe 11,000 something... but I hiked to the peak of Mount Rose outside of Tahoe. It just so happened the monarchs were migrating through at the time and it was the most incredible thing I've ever seen. There must've been millions of them everywhere. It was like a black cloud flying around us. So many were on the trees it looked like the trees were breathing.
Highest elevation so far Mt Whitney (14,505’, 4,421 m). Pretty uneventful climb since it was the end of over two weeks on the John Muir Trail. The previous 5 days was almost entirely avoid 10,000 ft. We slept on the shoulder of the mountain and sauntered up in the morning in about an hour.
Highest climb from the bottom to top was maybe Mt Williamson (14,379’, 4383 m). Trailhead is about 6300 ft, so at least 8,000 ft of climbing (2440 m). It was very difficult, climbed over 2 days. Not much time to adapt to the altitude. The hardest part was the realization that the top is exactly half way. I just wanted to paraglide down or get a helicopter ride. Some very difficult rocky terrain.
Honorable mention is Mauna Kea (4207 m). I had a magical elixir of coffee and Maca (REBBL Chocolate flavor), and powered to the top without altitude sickness. I haven’t tried it since, but I will try Maca again next time I’m going up in elevation above 10k ft.
