On the contrary, I have been writing and published for 60 years, and there is a vast difference between what passes for writing at school and university and what the publishing industry accepts.

Most authors (whether through traditional publishing houses or self-published) earn less than $1000 per year. As for content writing sites, from 27 long years of experience on the web, only the top 5% make it past the payment threshold. On Medium, that is changing, but only the top 5% earn more than $100 per month.

So, sorry, it is absolutely and utterly not something you can develop at any age. Writing is very much a talent, and if it was so easy, you wouldn't have all these people trying to figure out how to earn a living from it.