The world's most populous country has restricted most families to a single child since the late 1970s, but the Communist party said in November that couples would be allowed to have two offspring so long as one of the parents was an only child, rather than both.
Authorities had expected the change to result in more than 2 million extra births a year, but out of more than 11 million couples eligible, only 700,000 had applied for permission by the end of August, the China Daily newspaper said, citing the National Health and Family Planning Commission.
Of those, 620,000 had been authorized, it added.
China has a population of 1.36 billion, the National Bureau of Statistics said in January, but its working-age population fell by 2.44 million last year.
Over-60s accounted for 14.9 percent of the total, it said, and projections show that they will represent one in four of the population — 350 million people — by 2030.