How old you have to be to move from Canada to USA? (BC to California)?

Age is not relevant. Qualifying for a visa is your problem. How do you plan to qualify? For a young, uneducated, unskilled person, you have to qualify through your family. Your US citizen parent, sibling, or spouse will have to sponsor you.

Lisa is correct. Anyone of any age can apply for residency, although a minor must have approval of a parent or guardian (a person that has legal responsibility for the minor). If you want to visit, a Canadian has that right without needing a Visa or other documentation apart from their passport. However, if you wish to work or settle permanently (with "permanent" being defined as a definite length of time by law, although being an American citizen myself I don't know precisely what that limit is), then you have to do it through a formal application. If you go to the states without proper permission, and overstay the legal time limit OR work, you will be deported AND it is probable that you will be refused entry to the country in the future. I have a Canadian acquaintance that is barred from the US for that very reason (he lived and worked in Florida for a couple years before he was caught and barred for life from the US). What is worse is that he ended up later marrying a lady he had met down there, who moved to Canada, they had a kid, and now he cannot accompany his wife and child to visit her relatives in the states, unless something has changed since I last discussed it with him. Basically, you cannot legally just move to another country without permission, even between two countries that are as friendly and open as the US and Canada are.

are you sure you want to move to santa monica (i live 15 minutes from there)? it's expensive there so you have to have a good job to afford it and jobs aren't about nothing. just a one bedroom apt is $1100+ cause it's by the water-beach, so imagine a two bedroom.