Earlier quoted context omitted.
50 years. The wright brothers flew in 1903, by 1953 there had been tens (maybe even hundreds) of thousands of aircraft built, and millions of people had flown on them. Commercial jet aircraft and supersonic military aircraft were being introduced. Air travel was expensive but within the reach of even the middle class with some savings, 20 million people a year were flying. "Only fifty years", indeed.
Yet after another 50 years flying has not become all that much cheaper. Unlike flying reaching Mach 25 takes a ridiculous amount of energy and there is little reason to suspect it will become cheap in the next 50 years.
As far as manned spaceflight, it's certainly fundamentally more difficult than air travel but that doesn't explain the lack of progress the last 5 decades have seen under NASA leadership. Indeed, we're already seeing the first fruits of a properly open and competitive launch industry, something that hasn't generally been possible for most of the last half century, and it is already beginning to revolutionize manned spaceflight. In the next 50 years if the industry keeps advancing they will have developed streamlined mass produced launch vehicles (Iridium proved that such a thing was possible for satellites, at massive cost savings), single stage to orbit vehicles, and truly reusable launch vehicles, all of which will ultimately bring manned spaceflight into the reach of ordinary folks.