Confusion about まっとうに, 青春をする and the subject and object of this sentence

Question

I'm re-reading a light novel and I don't think I'm going to figure this sentence out anytime soon...

Quick context: one day a man meets a teenage girl, makes it clear that although he finds her cute, he has no interest in her romantically since she's too young.

Next day, he starts talking to her more and starts berating her, calling her stupid and disapproving of her lifestyle. Mid-tirade, it cuts to his thoughts. The first two quotes I understand, but the last one confuses me:

正面｛しょうめん｝から顔｛かお｝を見｛み｝ると、やはり可愛｛かわい｝い。

Actually, seeing her face head-on, she is pretty cute

どうして。俺｛おれ｝の中｛なか｝にそんな気持｛きも｝ちばかりがぐるぐると回｛まわ｝る。

Wait, why. Why are feelings like that all that's stirring inside me?

まっとうに青春｛せいしゅん｝をして、まっとうに恋｛こい｝をして。そういうふうに生｛い｝きられなかったのだろうか。

I honestly feel young and like I'm in love. Are those feelings there because I couldn't live like that I wonder?

From what I found, まっとうに means decently, honestly, seriously. And 青春｛せいしゅん｝をする means to feel young or be reminded of your youth. So if I guessed about the first part it'd be "She's so earnestly young", but then there's a 恋｛こい｝ out of nowhere. It doesn't make sense for him to have feelings for her- it's not brought up again for a while in the story and doesn't fit the current scene.

I'm really not sure who the subject is of the third quote or what the sentence means; I'm just not sure how to translate まっとうに　exactly and how the 青春｛せいしゅん｝をする,　恋｛こい｝をする, and　生｛い｝きられなかった connect to the situation and his thoughts.

Any help will be appreciated!

Answer 1

青春(を)する never means "to feel young" nor "to be reminded of your youth". It means something like "to enjoy the joys of youth" or "to spend one's youth in a satisfactory manner". まっとうに青春をする refers to spending a decent/ordinary life as a youth, which usually includes loving someone.

まっとうに青春をして、まっとうに恋をして。そういうふうに生きられなかったのだろうか。

Enjoying her youth like everyone does, and loving someone like everyone does... Couldn't she live like this?

So this man is not regretting his own life, but is worrying about the girl's life, right? Then the subject of this 生きる should be the girl. Here, he's probably thinking something like "A teenager girl who is objectively this cute should be able to spend her youth happily with someone, but why is she living in such a wasteful way?"