Although Brazilian was put on the C.I.T.I.E.S. treaty list of endangered species, and hence, was banned as an international item of trade, new, freshly logged Brazilian is readily available for sale.
The reason for this is that the Brazilian government has allowed the salvage of rosewood stumps to continue. There is still a lot of fine wood left in these stumps, but a lot of it is of such poor quality that many luthiers refuse to build with it.
Your concern should not be the age of the rosewood per se. Try to get straight grained, nice colour, and if possible, quarter sawn. Reis is right that the quarter sawn wood is very rare nowadays. I have some perfectly quartered 30 years old stuff. Once it's gone I'll probably not find stuff like it anymore.
But check out http://www.alliedlutherie.com
. These guys have a good web-site and specialize in salvaged brazilian rosewood. Some of thier brazilian is of excellent quality.