Good one. See post #1.
“Catholic School Girls Rule” - Red Hot Chili Peppers
There is no suggestion in that song that “Virginia” is underage. The point is, she is holding on to her virginity inappropriately long, and refusing to behave like a proper adult. (Of course the singer is not saying this for disinterested reasons, but that is another matter altogether.)
I nominate George Michael’s Father Figure, and having read the lyrics fully for the first time - eeewwww!
[del]High[/del]lowlights:
I will be your father figure - put your tiny hand in mine
But sometimes love can be mistaken - For a crime
ETA: missed the second page, been covered.
Tim McGraw has a song named “Seventeen” from his album named A Place In The Sun. Then of course Taylor Swift has her song named “Fifteen”. 
God bless you and her and Tim always!!!
Holly
Cherry Bomb by the Runaways. It’s told from the jailbait’s point of view.
If you’re going that route, isn’t “Hands Clean” by Alanis Morrisette the same?
Nitpick: 15 years old.
Also: at least one of the Stones apparently did think it was ok. Bassist Bill Wyman’s love life makes pertinent reading.
As does Ted Nugent’s and Jimmy Page’s. Both had underage girlfriends (Pele Massa and Lori Maddox, respectively) when they were in thier late twenties or older. I’m thinking Nugent got himself appointed her legal guardian so she could travel with him.
Yes, but they still love him in France. 
I always thought the magic rat’s girl in Jungleland by Bruce Springsteen was underage but now I’m not sure why. I guess the part about the rat driving “his sleek machine over the jersey state line” just felt especially significant.
… and I was just yankin’ y’all’s chain about Clair.
“Hey, Girrrrlllieeee!!!”
That’s Jerry Lewis(no Lee). Or I’ve been whooshed.
There was a very funny thread (google fu dead or missing) where a poster confused the two - key line being "Great balls of HEY LAAAADYYYYYY!!!
Yea I read it Must have just missed it. As soon as I read the question it poped into my head probably made me not see it in the list.
Jimmy Buffett’s “Livingston Saturday Night” isn’t about underage girls, but does contain this lyric:
Sing a song, play some pong, shoot a little pool,
Hittin’ on the honeys right out of high school.
Yeah, fifteen may get you twenty,
but that’s all right,
"Cause they’re rockin and a rollin’ on a
Livingston Saturday Night
From the country side:
Joni, Joni, Please Don’t Cry - Conway Twitty
Do creepy songs about deflowering girls count? If so:
I Can Tell You’ve Never Been This Far Before - Conway Twitty
Dragon - Are You Old Enough? (1978)
Dragon were a New Zealand band, also big in Australia at the time. (The street scenes at the start of the video are very obviously Melbourne.)
Probably Little T & A by The Rolling Stones, which features this suggestive lyric:
The pool’s in but the patio ain’t dry