There is no correlation. Greta is not in any meaningful way leading anything. She is just a reminder to change policy and take care of earth. Her purpose is to pressure and shame adults or policy makers.

On the other hand. 16 year olds in the majority of cases are adults. Nature says they're adults. That's why 16 year olds or even younger can become mothers. If we're saying they're not because their brains aren't fully developed then brains only finish growing when people are 25. Which means we should raise the Age of consent to 25.

There is no moral objection to marrying or having sex with 16 year olds but in some countries you can get in LEGAL trouble for it. Most countries including america allow people to marry 16 year olds or younger. https://www.youtube.com/watch?time_continue=2&v=yr1WnL070hc