I've seen reviews and/or book discussion threads where people comment or chat (often negatively) about series characters in crime fiction that do not seem to age.
One discussion (where and when and with whom I cannot recall) had worked out the supposed age of the Spenser character by Robert B. Parker. The gist was that by the time of said conversation (maybe around the release of second last Spenser novel fully written by Parker?) the sleuth would have to be somewhere around 60 or 65 years old. The person's point was that they had lost interest in the series by then because it was hard to believe that this character could still be kicking ass like a young guy.
In a similar but different vein, I read an interview somewhere long ago where Sue Grafton addresses the topic of Kinsey's age. Essentially, even though the Alphabet books come out roughly once a year or so, Kinsey was/is still fairly young. As I recall it, Grafton stated that the first book was set in Nineteen-Eighty-Something and that the subsequent novels carried on in that timeline.
This is more or less what I have done with the Sasha books.
Blood and Groom (released in November of 2009) takes place mainly during the the spring/early
summer in an unspecified year (contemporary, roughly 2009 or so). Dead Light District, the second book, which was released in March 2011, picks up roughly where Blood and Groom left off. Dead Light District starts in July of the same year and finishes right around Labour Day. The third book, The Lies Have It (released in November 2011) begins a few weeks after Dead Light, with the action taking place during October of the same year. I am currently working on book four (Frisky Business), and it takes place in November of the same year.
As you read through the series, you'll notice that Sasha refers to other cases as happening "a few weeks ago" or "last month" - she doesn't say years at all.
I like doing it this way. Having a bookworld timeline allows me (and the reader!) to grow along with Sasha. There are no gaps in her life, no blank spots for what she did over the last ~eleven months. This way, I also get to work with the seasons.
By the time I get to book five, it will be Christmas, and book six should be smack dab in the middle of winter, which makes a nice writing contrast from the stultifying humidity of a Toronto summer.
So, for the time being, Sasha is still in her early thirties and it's still 20XX. Maybe by book seven, I'll be ready to throw a birthday party for Sasha (it will have to be in August, as she is a Leo).