If you're curious about the age of your toilet, try this trick that our home inspector taught us. Look at the stamped date under the toilet tank lid: it will indicate the age of the toilet. In this case, 12 March 1987. 25 years seems like a good run for a toilet.
First, I shut off the water supply. I can't imagine that you would miss this step, but I might as well put a reminder here.
I then stuck some shims under the gaps to stop rocking, and tightened the nuts with a hand wrench. I tried to be careful not to over-tighten, because I didn't want to crack the bowl. I twisted each nut 1/2 turn, alternating between sides, until I didn't hear any sounds indicating shifting when I tried to rock the bowl. I didn't notice an increase in resistance when turning, so I think I was not overly aggressive.
I checked the alignment of the bowl to the wall one more time, just to make sure that nothing had shifted. Then I poured some water in the bowl to check for leaks and prevent gases from coming up the hole. Everything looked good, so I continued.
I then checked the position of the tank relative to the wall and its level, and shifted until I was satisfied. Then I tightened the nuts up from the underside.
And that's the story of our $10 toilet. Isn't she pretty?