The song Blowing in the Wind has the following lines

How many roads must a man walk down
Before they call him a man

I have no clue what this means

How many seas must a white dove sail
Before she sleeps in the sand

This seems to refer (metaphorically) to (involuntary) human euthanasia

How many years can some people exist
Before they're allowed to be free

However, this refers much more strongly to euthanasia (people, free instead of dove, sleep) with the exception of "can", which slighlty implies being natural death.

Can someone explain the above couplets?