The H-index is a measure of scientific research output defined as the number h of publications that have been cited h times or more ( http://en.wikipedia.org/wiki/H-index). Thus an H-index of 10 indicates that 10 publications have been cited 10 times or more. The index is designed to improve upon simpler measures such as the total number of citations or publications to give a measure of both productivity and impact of published work. The index works properly only for comparing scientists working in the same field; citation conventions differ widely among different fields.
My total citations per year
Google Scholar provides an estimate of the H-index as part of my Google Scholar Profile (http://scholar.google.ch/citations?user=qlhV1WcAAAAJ&hl=en). This is calculated by a computer program and may not be entirely accurate, you need at minimum to check that Google Scholar is correctly identifying your publications and not missing some or including works that are not yours.
The H-index increases with years of active publication and there have been proposals to adjust it by dividing by career-years to give a more comparative measure across researchers of different ages. However, its not always simple to define career-years, particularly for people who have had periods in and out of active research.
A few years ago, I noticed that my H-index was a not far off my age, and took some interest in watching to see whether it could overtake my age. Which it did about a year and half ago. My H-index is now 67 as at the time of this post, and in total my publications have received 44,003 citations. So maybe the new benchmark for H-index is to exceed your age.
JE Hirsch, the author of the h index estimated that after 20 years a “successful scientist” will have an h-index of 20, an “outstanding scientist” an h-index of 40, and a “truly unique” individual an h-index of 60a. However, he pointed out that values of h will vary between different fields. Well, I do appreciate confirmation that I am a truly unique individual, but suspect that apart from Google Scholar possibly estimating H on the high side, I am in a field (producing global health statistics) which by its nature will generate lots of citations. Helped along by the medical academics always wanting to provide a global context or a projection in the introductory paragraph of their paper on a particular disease.
Colin Mathers 
A little over a year later and my H-index has reached 75.
The notion that your h-index matching your age needs to be the new bar is absurd. Good for the author that his does. But dear author, did you have a h-index of 20 when you were 20? Don’t generalize your individual experience to all of science.
Ling, I agree with you, it was but a light-hearted suggestion. I noticed some years ago that my H-index was only a little lower than my age, and made it a silly goal to get it to my age (of course, there is really nothing I could do to actually make that happen). And I am well aware that average H-index varies quite a lot according to discipline and that I have happened to work in a field where there is great interest in the sort of work I do in global health statistics. I’ve been quite amused to see arcane papers on the cell biology of intestinal lining cells start off with a reference to the global burden of intestinal disease. It seems to be a medical tradition.