Anytime I hear someone like ~17-21 exclaim they're in true love I can't help but mentally laugh. It's like hearing a toddler say they finished some calculus homework.
Sure a genius kid could exist 1 in a million and really do that math but most likely that young person has no clue what romantic love is, they just want to know or think they do.
Uhh I disagree with this.
If you mean true love as in lifelong relationship, then probably, as it's rare for couples to last from teens to oldage. But feelings? The very hormonal state of a teenager makes it so feelings are extremely powerful, they most certainly do love and do it quite strongly too. Same for the bad feelings too, of course.
It might be immature to believe that their love will last forever, that nothing'll ever change, but the feelings are sincere and deep.