Home sales across the United States fell in December for the first time in four months amid higher prices and low housing stock continued to shut out first-time buyers. First-time buyers accounted for 30 percent of sales last month, compared to 31 percent a year ago. The availability of existing houses fell to the lowest level in more than two decades. Existing home sales dropped 4.6 percent to a seasonally adjusted annual rate of 6.18 million units last month, according to the National Association of Realtors in a report on Jan. 20. Economists polled by Reuters predicted that sales would fall to a rate of 6.44 million units. However, demand for homes remains high, according to the association. Median housing prices jumped 15.8 percent from a year ago to $358,000 in December. House prices averaged a record $346,900 in 2021, up 16.9 percent in 2020. Homes sold in an average …