If you accelerate at 1g it takes less than a year to get to the speed of light (almost to the speed of light, you can't ever actually get to light speed). So, that would take 4 years to speed up and slow down coming and going, plus the additional time traveling at the speed of light to cover the distance, but minus the slow down in time that you experience when close to the speed of light. Perhaps the 7 years figure the poster cited came from a calculation of this sort. At any rate, time on the earth will not slow down and everyone here would be much more than 7 years older when you get back.
Now all we have to do is invent a spaceship that can get to 99+% of light speed.
Nope, the other way around. Ignoring for the moment the time required to accelerate and decelerate, the 7 year round trip is in Earth's time frame reference.
The passenger on board the space craft will experience less than 7 years travel time. How much less depends solely on how close to C the rocket travels.
Earth cannot experience more than 7 years of time passage.
Exactly. I believe Einstien said that if you achieved the speed of light to you, the moving object, time seems relative. Everything appears normal to you but the world around you is changing. In other words, as I understand it if you’re in some kind of craft traveling at the speed of light, your on board clock is telling the time, relative to you but outside your craft time is speeding past.