Probably because all the candidates, suck.
Why do young adults not vote do you think?
Generally speaking, politics for young adults is like wine for young teens; it is an aquired, mature flavour that needs to come naturally, sometimes never does but generally you take an intetest sooner or later.
If you mean legally, it's because they're too influenced by their parents and wouldn't be able to make decisions uninfluenced by others.
