Alpha Centauri is 4.22 light years from Earth. A single light is around six trillion miles. If you intend on coming back you’d have to square that distance. That’s going to be a lot longer, either way then just 7 years.
As I said, running the numbers at web calculators for just this purpose, and you come up with 7 years (round trip) for the traveler and 15 for those back home. The operational presumption is 1-G constant acceleration to about 90% ‘c’. This takes 1 year (for the traveler, I believe). Thus, accelerate 1 year, decelerate 1 year, visit AC, accelerate 1 year, decelerate 1 year, back home and visit the remaining relatives that aged about double what you, as traveler, have aged.
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.
Better hurry..... the Greenies say we're toast in around 12.