what year is it in the books?

Warriors started in 2003. We know for sure that 10 years have past since Rusty first joined the clans. Puting the current story around the year 2013(ignore the fact that we are in 2016). Alderpaw's journey would be in 2012/2013

Here are some other plot points we know about:
2000: Tallstar's revenge(we know this takes place 3 years before Rusty joins Thunderclan.)
1933-ish: The Ancients left the lake 70 years prior to Rusty joining Thunderclan.

It was originally believed that the clans five clans formed in the forest around 1973, 30 years prior to the beginning of our main story. But this was contradicted by the dawn of the clans story arc.(the clans have probably been in the forest closer to 50 years, putting their formation around 1953)

Does this help?