It all depends. Some people are more mature at 19 than some at 25 or visa versa. Maturity, responsibility, trust, commitment and love are very important when deciding to settle down and marry someone. It's a huge step to take. It also helps to be financially smart. If you know in your heart that you want to marry this person then do it but just know marriage takes work by both partys.
There will be bumps in the road ahead, be prepared to communicate constantly with your partner. Enjoy each other :)