For me it is motorized flight. It was only in 1903 that the Wright Brothers succeeded in getting a plane off the ground under its own power. In 1909 a Frenchman was able to cross the English Channel in a plane. During the First World War you had your first specialized planes. You had observers, fighters, bombers, seaplanes and planes capable of being launched from ships. Think how short a space of time all this happened in yet there was more to come.
After the war there was the beginning of the air mail runs. Men and women were venturing farther in better designed aircraft. 'Smithy', an Australian adventurer, flew from the USA to Australia. Then there were the adventures of the American aviatrix Amelia Earhart. She was the first woman to fly across the USA.
During the 2nd World War you had the development of rocket and jet planes. Certainly by the time I was born it was possible to fly by commercial jet from Australia to the USA or anywhere else in the world. And it doesn't stop there!
In 1969 I went home from school to watch the first moon landing and to actually watch men step onto its surface. Exciting? You bet! But think on it a minute. From 1903 to 1969...Not a great distance in time. Yet there was more to come.
Before the century was out you had man made satellites in space and one man made probe sent out which is, as I write, about to leave our solar system for the truly unknown.
Is that enough for you? If not then check out my hub on early motorized flight or get your wow meter fixed.
My grandfather was born late in the 19th Century and passed away in the 1970s. He lived long enough to see planes go from glorified death traps to contraptions capable of taking you just about anywhere in safety. (Yes there have been jet crashes but generally it is either pilot error or poor maintenance responsible.) So what am I likely to see and experience in my lifetime that I haven't seen and experienced already when it comes to flight? Good question. I can't wait to find out.