Does anyone know anything about breeding budgies? I've never had any success I've had budgies for 10+ years and never had them breed

ATM I have 2 6month olds ( I'm guessing too young 1m 1f)

1 3yo male and 1 1yo female

They get seed, grass, fruit, veggie scraps, a cuttle bone

They have a nesting box inside sitting on shelf I hardly go outside to see them other than once a day for food and water so there not being overly disturbed

They live outside in an aviary size of a shed with 2 button quails

What am I missing?