I have repeated this many times that Sikh scripture is more of a spiritual guidance than a book of hard and fast rules defining certain terms like who is a child and who is a young woman. So in Sikhi a child is child as per standard definition and there would no other definition of a young woman than the standard definition.
1) What is a 'child' who has menses/wet dreams?
definition of a child as per wikipedia:
# Child:
* Infant (baby) (ages 0 - 1.5)
o Neonate (newborn) in the first month of life
* Toddler (ages 1.5 - 4)
* Middle childhood (schoolchild (or schoolboy or schoolgirl)) - Primary school/Elementary school age (ages 4 - 11)
o prepubescence, a subset of the above (ages 10 - 11, approximately)
* Preadolescence (preteen, or late childhood) - in the United States, middle school age (ages 11 - 14, approximately. Note overlap with prepubesent stage of middle childhood.)
# Adolescence and puberty (teenager) (13-18)
2) How does sikhism differentiate between someone who's old enough to get married or if someones your child. Please quote evidence from your religious sources.
Once again, Sikhi, being pure spirituality, only concentrates on how to be spiritually wiser rather. But it's common sense. If someone is about the same age as your children or children of people of about the same age as you.
3) How does a person reach the next level and be with God if the guru before him never had those laws? And who gives the guidelines to the vices, what is permitted or not?
As far as my understanding goes, first level is to control vices and revering at God's name. What do you mean guru never had those laws? It isn't matter of what's permitted and what's not. It's more of a matter of what you have controlled what you haven't and you can only know only through spiritual experience.
4) Can anyone simply decide what a vice is? For example, right at the beginning of the thread we hear cali dude saying that marriage isn't permitted because lust isn't permitted either - as its a vice. Now if lust isn't permitted, then does the couple have intimate relations for no other purpose except for kids? And if the guy starts liking his wife, that's sinful right? Because lust isn't permitted. So does that mean he's getting less karma points for desiring his own wife?
No, people can't simply decide what a vice is. A vice is whatever distracts our concentration with God. It isn't matter of what if in a marriage. The one who has lust can't get to that level within or without marriage.
5) How will the people unite with God according to the sikhi beliefs, because the flame idea doesn't make sense. Either the smaller flame joins in with the bigger flame and becomes that bigger flame, and if that is the case - then isn't that saying God isn't complete, i.e. Perfect?
Flame concept is a example, just as water blended with water, an example to explain how close to God gurus and saints were, so close that they are become blended with God. God is complete with or without anybody. God isn't less of a God without someone and isn't more of a God with someone.