Dear Lucy,  

What I have found over the years is that while God's plan for each soul is special there are still some general things that happen to almost everybody.  

First is the inclination, interest, openness. You have that.  

Then the fears, you have them too.  

Then the moment of contact, when you meet the people or find that place that makes you ask, 'maybe here?' You have not reached this point yet. Let me assure you, that when you do all the other questions such as family, local parish community, personal ideas as regards what you would like to do, etc.. will all fall into place.  

Some who have a vocation go directly from High School into it. Some enter after college, either Catholic or secular, there is no general rule, it depends on when God calls you, and believe me, he knows when it is best.  

If you are 17 when you graduate you will also need your parents' permission if you want to enter a convent right away.  

My best advice to you now is to pray very specifically for your vocation: tell Jesus you want to give yourself completely to him, and ask him to show you where.