In Frankfurt, masked demonstrators reportedly looted at least two shops and damaged several others.
Police said protesters also threw petrol bombs at emergency responders as authorities tried to bring the situation under control.
The demonstrations were organised under the campaign “Gen Z regelt” and took place in cities including Berlin, Frankfurt and Munich.
Organisers said young people were protesting against mandatory military service and calling for greater investment in education, arguing that rising living costs were placing an increasing burden on younger generations.
The organisers had expected around 182,000 people to take part. However, police estimated that approximately 18,000 people demonstrated in Frankfurt, Munich and Berlin combined.
Protesters accused the government of failing to address young people's concerns while pursuing spending cuts and placing additional financial pressure on the public.
The movement has also faced questions over whether it represents an independent youth campaign or is backed by political and social organisations. Germany’s National Student Organisation, BSZ, distanced itself from the campaign and announced plans for a separate protest on November 20.
The demonstrations come as Germany faces economic growth challenges, increasing pressure on its pension system and difficulties in public services linked to an ageing population.