He was named Duke of York in 1611 after overcoming this early weakness (the picture depicts him in the year he obtained that title). When Henry died in 1612, Charles became the heir and Prince of Wales, as this official biography from the website of the British Monarchy indicates.
He also inherited the marriage negotiations for the hand of the Infanta of Spain. James I's proposal that his heir marry the princess of an old ally infuriated the Puritans in Parliament. There is a new novel from Sophia Institute Press about that planned marriage--which did not occur. Read more about The Spanish Match here.
Charles became king when his father died on March 27, 1625 and of course he did marry a Catholic princess: of France.