This report on "Beginning Farmers and Ranchers" was released just last week...

USDA defines beginning farmers and ranchers as those who have operated a farm or ranch for 10 years or less either as a sole operator or with others who have operated a farm or ranch for 10 years or less. Beginning farmers tend to be younger than established farmers and to operate smaller farms or ranches, some of which may provide no annual production.
Beginning farmers often face obstacles getting started, including high startup costs and limited availability of land. USDA—through the Farm Service Agency and the Natural Resources Conservation Service—provides loans and conservation assistance to beginning farmers and ranchers. This report draws on data from annual surveys and the Census of Agriculture to provide policymakers with a better understanding of beginning farmers and ranchers, including how they contribute to U.S. agricultural production.
Released Friday, May 15, 2009
Exerpt:
There are good reasons why so few farmers are young and many beginning farmers are middle-aged. Foremost among these reasons is that the startup costs in agriculture present a barrier to entry for some. Farming commonly requires control over a signifi cant amount of land and capital, and beginning farmers and ranchers face significant startup requirements. For example, it is only when farms gross at least $50,000 in value of production that most farms make a profi t, and the average asset base of farms with sales of $50,000 or more in 2007 was over $1.9 million. One way that beginning farmers acquire assets is through inheritance. Since farmers are living longer, like the general population, the delay in the inheritance of their heirs is likely a factor in the declining number of young farmers. In addition, it is not uncommon for an inheritance of farm assets to be split among multiple family members. This practice increases the likelihood that each heir will receive a share of farm assets that cannot support a family in farming. For those aspiring to enter farming without the expectation of an inheritance or in need of expanded acreage, farming may have to be postponed until significant resources have been accumulated to acquire necessary farm assets—a process that can take years. Aside from the financial challenge of acquiring land, beginning farmers and ranchers may also face tight land markets because farmland is simply not available for either purchase or rent within their local area.
For more information, see: http://www.ers.usda.gov/Publications/EIB53/
You can download the report here: http://www.ers.usda.gov/Publications/EIB53/EIB53.pdf