Herein lies a fundamental difference in worldview. A liberal would say: well, let people who want to get married and have kids do that, and people who don't want to get married and have kids can do that. No need for coercive social norms. In a vacuum, that sounds true. But a conservative would say: how can you be so sure that those social norms aren't helping people who ultimately want to get married to do so and stay married? The idea that societal happiness is maximized by maximum personal freedom and the total absence of social coercion is not obviously true.
There are life happiness benefits to older people helping younger people know what to look for in a spouse, and setting expectations about marriage and life in general. There are benefits and efficiencies that come from people of a similar age having kids at the same time. There are benefits that accrue from people being involved in supporting each others' marriages. My wife and I got married and had kids in our mid 20s--average for Americans in general but pretty early among our demographic (college-educated coastal urbanites). We didn't realize it at the time, but living in DC/NYC we were pretty miserable. Nobody our age had kids and it was very isolating. We were so much happier after we moved to a more socially traditional exurban place where other people our age also had kids, peoples' parents were actively involved in helping them raise their children, etc.