Personally I think it is after getting to know a woman more who married when she was 16 and gave birth when she was 18.
Divorced at 20 and only enrolled in Uni / got employed part time at the age of 24.
She realies heavily on support from her family and told me personally her life's been a struggle, fair enough but I hate how she doesn't think it's partly her fault
(or maybe she knows it but she's too proud to admit it)
You shouldn't make any big decisions like that until you're 21, at least. Even then, you should spend a year or so thinking about if that's really what you want. This isn't just for marriage/children either - I would recommend the same for leaving a job, applying for a job (in some cases), becoming religious, changing religion, becoming atheist, leaving the country, leaving the planet, joining the army, getting ordained, and becoming a supernatural entity.