Is dating a girl 3 years younger than me a bad idea if I'm 19?

Age does not matter! However, she is still a minor. Keep in mind that relevantly she will be less mature than you, keep your relationship status on the low side. And please do not take advantage of her. 3 years isnt a big difference but its on the edge.Good Luck!

It's not a question of it "being a bad idea"...it should be a question of "what does the law say if we..."!  First question is: Do her parents know?  Do they know you, approve of you, and know your age?  If they do, then dating is fine BUT, I wouldn't take anything any farther until she's 18! 
If she truly loves and cares for you, she will be understanding of this and not want your future to be placed in jeopardy with a statutory rape conviction or a sexual predator label...and it stays there for the rest of your life!  It's not ultimately up to her...it's YOUR decision in the end!

No it's not bad at all I met my boyfriend when I was 15 almost 16 and he was 19 we have been together for almost two years now and everythings perfect just treat her good,be honost with eachother etc,.. Age is no problem its just a number, as long as you treat eachother with the most respect you can youll be fine...best luck to you follow your heart not peoples judgements

No, not at all. 19 and 16 matches perfectly.

Let it be... Wait till she is older ?!!

Age doesn't  matter!!

Yes it is bad idea.  You might regret it later on.

If it's love that you have then no it's perfectly fine

I think is not a bad idea when a girl can date younger guy then you too can do that. Go dude and have fun with her. Good luck!

Thank you everyone, Most of the answers I got in this post helped me. I have decided to date her however I will not do anything sexually with her (not even if she initiates it) I will wait until (at least) 18. Again thank all of you.

It's not neccessarily a bad idea.  3 years is not a big age gap.  But keep in mind she is a lot more immature than you .  So please be a gentleman and do not take advantage of her . 

Dating is fine, but anything beyond that with her is a jail sentance. Be careful because you are an adult in the eyes of the law and she is not. You pay the price even if she initiate it.

Ooohh, watch out bubba your fixing to have a really bad one. You do anything with her, & you'll be up on child molestation charges. Leave it be.

Well thats not exactly against the Law here in the UK as the legal age of concent is infact 16 years old, so in your case then your 19 and she is 16 which to me isnt a great deal in that atall, it would ofcoarse perhaps be a moral dilemia for someone who was a conciderable bit older, but in your case then its not so bad I guess, she could be really mature and you could be really imature so when you put the slight age gap then its not so bad I guess