Coupla things I'd like to kick in here about for ya.
First, it doesn't matter how long you may last if she's not enjoying what you're doing. Don't be quite so concerned about quantity, learn how to go with the flow and enjoy the quality of the experience.
ESPenis EnlargementCIALLY if it's your first time!
One of the sexiest things about makin' love to a new gal is what I call "fit and rhytHydromax" ; every body is unique, to an extent, and exploring those delicious differences (ESPenis EnlargementCIALLY if it's your first time) is a large part of what brings the joy to sex.
Next : Just like the Kinks said, "Paranoia will destroy ya" (yeah: I'm that old) nervousness is an almost guarantee of a crappy time. Relax, relax, relax....and then relax some more. Lotsa times we (guys) get all caught up in the mechanics of sex and forget that it's a kind of elaborate dance...meaning that BOTH of you should be equal partners in learning what works and what doesn't. Don't focus on the destination: just enjoy the trip. And let nature work her wonder.
Last, as far as I've ever been able to figure, there's only three ways to get really good at anything:
1. Practice
2. Practice
3. Practice
So, if this is your first time, and especially if she knows it too, make a game out of playin' the game. Makin' love is nothin' if not a whole shitload of fun !! If it ain't, for either partner, for whatever reasons, then something is wrong or somebody's not taking the best approach to it.
Besides, you're 19 for Christ's sake! Even if you only last 30 seconds you can practice again in about another thirty seconds... for about two dozen times in one day !!
Oh, and did I mention: RELAX !!
Good luck !