I started menstruation from an early age of 11 years. Was fasting mandatory for me from such an early age? Actually now I am fulfilling Qaza fasting and hence confused from what age I shall calculate all the missed fasting. Please guide me.

Answered according to Hanafi Fiqh by Darulifta-Deoband.org

بسم الله الرحمن الرحيم

(Fatwa: 350/358/L=03/1436)

You turned adult after you experienced menstruation and fasting was obligatory on you from then. You shall make qaza of your fasts from that time.
قال فى الدر المختار: بلوغ الغلام بالاحتلام والاحبال والانزال والأصل هوالإنزال والجارية بالاحتلام والحيض والحبل….. (درمختار مع الشامى: 9/225)

Allah knows Best!

Darul Ifta,
Darul Uloom Deoband