I am also making up for 18 years of praying, I read them short after watching sheikh Mohammad al-hilli YouTube where he describes the wajib acts duas. I’m now in doubt if my prayer were fard on me from age 9 or when my menses started?

What is your advice for salat up Layl or just witr, should I start them or first pray all my qadha?

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If you follow sayed Sistani, you count from 9 hijri.

You can pray the midnight prayer or recommended prayers and make up the missed prayers at the same time. Pray your missed prayers after midnight then do the shaf’ and witr on their own.