Anyone who decides he wants to be an AFL footballer should have a footy in his hands for hours a day, every day, from the day he decides it. Bounce the ball: right hand, left hand. Drill your kicking. Learn and apply the correct techniques, even if they feel unnatural to begin with (especially then). Double-down if you're lucky enough to get drafted. (Barassi used to give his players a footy each. Old school.)
Some blokes can't kick because they're *smile*; others don't put the work in. That's my opinion. So, you wanna be a footballer? Do you sleep with your footy? Do you drill your skills? Can you hit a 45-degree lead on the tit with a low skimmer from 40 metres, off either wing, while running at pace with a bad guy up your clacker? Do you even use your opposite foot at training? Do you run laps bouncing a ball with either hand? Do you wanna be a footballer or not?
Soccer kids are drilled. Skills, skills, skills. They get (or did in my day) certificates for achieving certain competencies. It's something to aim at, and you don't progress until you can do it.
No doubt it helps to start at 12, or younger. Maybe there comes a point when incorrect muscle memory is just too deeply ingrained. Sure, some have better coordination and motor skills. But it sure as sh!t shouldn't be the job of coaches at the professional level to teach professional footballers how to kick a goddamn football.
If you can't kick a football, how badly do you really want to be a footballer?