10-14 days after sex should be fine, might take longer though deopending on your body, it took over 1 month for a store bought test said positive, i had to go to a doctor for a blood test to know.. and no there is no age limit lol
i mean if you really think about it, why would there be? why would they want to prevent younger girls from knowing if they are pregnant? all that would happen is mor unhealthy babys, because girls would be too scared to tell there parents, especially if they cant take a test and be sure, and then they would wait till there 5 or 6 months and showing till there parents realise it and they get any prenatal care