China's new policy to allow couples to have two children makes little difference to Peng Yajun. The Guangdong office worker, 36 and soon to be married, wants only one child as any more would be too expensive. "I'm an only child, I cannot afford school fees for two children and the cost of taking care of my ageing parents," she sighed. READ MORE: Five things you need to know about China's one-child policy The National Health and Family Planning Commission on Friday said the two-child policy would help cope with an ageing population and weakening traditional family support. The commission said about 90 million couples would be eligible and the peak number of births a year would rise to 20 million, from 16.87 million in 2014. It expected the labour force - those aged from 15 to 59 years - to rise by 30 million by 2050. It expected the population to rise to 1.45 billion by 2030, from 1.37 billion last year. But experts said this would not be enough to reverse the rapid ageing of the population. The government needed to act swiftly to encourage couples to have more children, expand the pension scheme and defer the retirement age, they said. Over 60s will make up 39 per cent of the population by 2050, compared with 15 per cent now, according to official data. Socio-economic reasons would dissuade most couples from having more than one child, demographers said. On some estimates, raising a child on the mainland costs about 20,000 yuan (HK$24,000) a year - more than 40 per cent of the average household income. Wang Feng, a demographer with the University of California, Irvine, said said China would have to learn from its neighbours in East Asia, which has one of the lowest birth rates in the world, to encourage couples to have more children and to cope with an ageing society. He said the government had started to extend pension coverage and raise the retirement age for some women in the civil service, but more was needed. READ MORE: ‘That’s great! But…’: Chinese residents respond to long-awaited lifting of one-child policy When the government introduced the one-child policy in 1980, it pledged to care for the elderly. If this was an "empty promise", it could lose support, Wang said. "The government should recognise this could be one of its greatest challenges. If it cannot deliver adequate support, given ordinary people have already made a huge sacrifice, it would challenge its legitimacy." Cai Yong, a demographer at the University of North Carolina, said the policy was "too little, too late", adding that demographers had lobbied Beijing for years to lift the one-child restrictions. It should have come in 10 years ago, before many young rural residents moved to cities, as they now faced the same economic pressures. He said about 60 per cent of rural residents between the ages of 20 and 30 were now living in cities and faced the same kind of socio-economic pressures as urban citizens, and they, too, had little incentives to have children. Experts say the impact of the additional births will be minimal. Wang said the projected peak figure of 20 million births a year was still lower than levels of 26 million in the 1980s. "The long-term demographic effect is going to be negligible," Wang said. “The new policy is more political and humanistic than demographic.” Cai said 20 million births a year would bring the fertility rate – the average number of children a woman can expect to have in her lifetime – to 1.8, from 1.5 now, but still below the 2.1 needed to keep the population stable. But the policy was still “an important step forward” because it would grant people more personal and social freedom, he said.