Well, before I start again, I don't think it's actually possible to return to an Ancient Greece kind of society, or not on short notice and not on any scale that matters. Now maybe if we had some post-apocalyptic society re-discovering social order and culture in that way, it would be possible, but otherwise the USA isn't going to turn into Ancient Greece any time soon.
And therefore I also don't feel any need to redefine or excuse Ancient Greece.
That said, well, first of all it depends on exactly where and when in Greece are we talking about. We're talking hundreds of autonomous city states, with different cultures and customs, and over a thousand years, and whole culture blocks as different as the original Achaeans vs the later Dorians. It's not going to be the same culture any more than one could treat 2010 Los Angeles culture as the same as the 1620 Plymouth culture and the 1000 AD Vinland culture. You get the idea.
That said, I think a good case can be made that most literally meant homosexuality.
For a start even the lexicon and speeches built around it, make it clear that they really meant erotic attraction or love. While, again, across time and space it varied whether you're also allowed to have sex, or what kind of sex, the attraction to the younger protege was supposed to be basically erotic anyway. Basically, "Love of youth" only in as much as by "love" you mean sexual arousal.
Also "of youth", only in as much as by "youth" you mean "boys". While the terms used are a bit more gender neutral, pretty much everything we know about it shows that it almost never applied to girls.
So, sure, at some times and in some places you may not have been allowed to actually have sex, but as a man you were supposed to be sexually aroused by boy. I think that's by definition gay.
And not only they presented it as something acceptable, but it was even freaking _patriotic_ and the last defense of democracy to be gay. Yeah, they didn't spare the grandstating. Apparently getting a boner at a young boy's ass was outright feared by tyrants everywhere. (See, for example, Plato.) In fact, if you listened to them, tyrants were getting ousted by pederastic couples all over the place. (See, Hieronymus.)
That said, there is plenty of indication that at plenty of times and places it was allowed to have a lot more than some chaste kinda puppy love. For a start there is no shortage of representations of some guy reaching for some kid's genitals, or some really affectionate kissing, and whatnot.
And then we have accounts like that of Aristotle, which claims that for example the Cretans encourages this kinda thing to keep the men away from the women, so they'd bear less children. I.e., as population control. Unless sex was involved, I failed to see what kept the guys from going home and boning the wife afterwards.
And then there is the case of the preemptive lawsuit by Aeschines against Timarchus, to strip him of citizenship and thus prevent him from filing a suit against Aeschines. (Otherwise, obviously Aeschines couldn't care less about Timarchus' love life.) Aeschines makes it clear that Timarchus continued to be the "beloved" of many rich people, after reaching adulthood. But the more interesting part is something else. The interesting part is that basically Aeschines feels a need to go into damage control mode there, so to speak, and limit the offense that might be perceived by many from his accusation. Aeschines obviously feels a need to make it clear that he's not condemning the institution, and even says that he himself had had lots of boys as "beloved" and even got into scrapes over them, but not for money. The extent of the crime he gives Timarchus is strictly that he was a free man working as a prostitute.
Essentially what he's feeling a need to add to that speech is,you know, wouldn't want those guys to think he'd be as un-greek as not being a gay pedophile.