First of all, science is provisional. You go with what you've got, until you've got something better.
Bill and sithgoblin's posts have very important points, and I suggest you have a good look at them.
With regards to the age of the universe; you should probably talk to astronomers and astrophysicists (or 3rd year uni students looking at a future in those fields... like me

). And so I shall correct you.
Einstein, in 1905, assumed that the speed of light in a vacuum was constant (it was; speed ~186,000 miles per second, or ~300,000 kilometers per second). Thus, one can take a lightyear as a unit of measurement (the distance light travels in a year), of the order of 10^12 meters.
Since the speed of light is constant, and because of the Doppler effect (I won't bother explaining it here), we can determine the distance of the farthest stars that we can see. Working backwards from this result, we can then determine how long the light has been travelling, and if you crunch all the numbers, I believe you end up being able to see about 14 billion years into the past.
Yes, you heard me right - into the past. When you look at a star in the night sky, it isn't there. It is actually, right now, in a different position. What we see is the light that was emitted some time ago (nearest star is 4.2 lightyears away, so we see that star as and when it was 4.2 years ago). And that is how we calculate the age of the universe.
And physics is generally a lot more exacting as a science (except with quantum mechanics... but lets not go there).
Do hope you'll pardon the numbers though.