The typical age is 16-21. Models can be younger than this, but many agencies will require models to be at least 16. Likewise, models can be older but agencies and clients tend to like their models looking younger and more youthful.
Once you have 10k followers, Instagram will make it easier for you to get people to your website via Stories with the swipe up to link feature. Swipe up is the only way to get a direct link from your Instagram to your other web properties. And, it’s available in STORIES, if you have 10k followers.