A few years ago I may reached the age of it being obligatory to fast Ramadan but I didn’t know at the time, the problem is I am not sure when exactly it happened so I am unsure how many Ramadan’s I have missed so I don’t know how much I have to fast, and I am not even sure if the sign that appeared made me have to fast. If it matters I follow the malikiyah madhab
Wa’alaykum as Salam wa rahamtullahi wa barakatuhu,
You should first try to apply your mind and think when exactly have you attained puberty.
If you are really unable to ascertain when you reached puberty, then you should consider your puberty from the age of nine lunar years (approximately 8 years and 9 months when using the solar calendar).
You should therefore make up for the fasts that you missed from then.
And Allaah Ta’aala knows best
Ismail Moosa (Mufti)
السن الأدنى للبلوغ الذي لا تصح دعوى البلوغ قبله :
21 – السن الأدنى للبلوغ في الذكر : عند المالكية والشافعية باستكمال تسع سنين قمرية (الموسوعة الفقهية الكويتية – 8/ 192)
This answer was collected from Fatwaa.com which is an excellent Q&A site managed by Mufti Ismail Moosa from South Africa. .