cut (one's) teeth in (something)
To gain experience with something, especially at a young age. A reference to one's teeth coming in when one is a child. Jen may be young, but she cut her teeth in academic writing, so her perspective and expertise will be invaluable to us.
cut your ˈteeth on something
learn or gain experience from something: It was a small experimental theatre company and many of today’s most successful actors cut their teeth there.