Financial dependency can not be fixed under a time frame... I know people who do part time jobs during their college days. So financial stability can never be bench marked. It depends purely on every individuals satisfactory limit. Mentally matured to handle a person at 18, YES that is a valid question. Coz, Handling people needs experience and if there are going to be negative events happening at 18, can definitely dampen a Human's rest of Life. So, people has to learn things, until every human comes to a point where S/He feels, Yes, I can Handle myself in any situations, and then opt for a partner to live with. Living together doesnt mean only physical relationship. It definitely needs more of mental maturity to be with people...