Which factor has contributed to increase in the timespan for adolescence during the last century?

One significant factor contributing to the increased timespan for adolescence over the last century is the expansion of education and the prolonged duration of schooling. As higher education has become more accessible and often necessary for better job prospects, young people are spending more time in academic settings. Additionally, societal shifts towards later marriage and childbearing have extended the period of adolescence, allowing individuals to explore identity and personal development before assuming adult responsibilities.