meaning of being an adult

People in Japan think when people turn the age
of 20 years old, then they are regarded as an adult.
from then, people can smoke, can drink alcohol
and can vote in an election.

next year, I will get various rights when we turn 20.

but what exactly is the meaning of being an adult??

i think the point is not the age.

even people aged 20 and older,

sometimes don't look like grownup.

i mean..not about the looking, but inner.

i don't wanna be like that,

so i will continue lifelong learning to be an adult.