Here is a theory, Software as a Culture and Info vehicle is pretty much mature, the social, the news, etc. An average 20 year old is not well equipped with deep domain knowledge, a good example is flexport, I do not know much about founders but its a business, you need to have a deeper understanding where a 30+ would usually have. So, you will see start-up coming from much older people at the helm and not the younger people. May be this is my bias, but Software fed a cultural need, a communication and information need, we are moving into different realms. Realms which are distributed across the country and world and over all need DEPTH(in Domain) rather than horizontal trends.