Sorry, I sould have read all the posts in this thread before I replied.
The Philosopher's Strone was published in 1997 (I think) in the UK; the Sorcerer's Stone was published a year later in the US.

As for Harry's age, most people figure Harry was born in 1980, because in book 2, Nearly Headless Nick's 500th deathday cake gave the year of his death, and Harry was 11 at the time, so you can use that to figure out when the books are taking place.
Is this making sense?
If you want more evidence, when Harry visits his parents' graves, the headstone says they died in 1981. And Harry was 1 year old they died.