18 isn’t too old to start modelling, though it may limit your options — certainly you’re unlikely to make it as a professional editorial model if your first experience of the industry dosn’t come until you’re 18+.
What happens after 10k followers on Instagram?
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.