Were ancient people more bisexual than modern people? Watch
The classical Romans did rail against effeminacy, but interestingly enough there are quite a few references to men putting on makeup because they want to attract women. Here is a passage from Pseudo-Lucian's Affairs of the Heart, recounting a debate between two men about the relative merits of women and youths
He was also a devotee of physical training, though in my opinion he was only fond of the wrestling-schools because of his love for boys. For he was enthusiastic only for that, while his hatred for women made him often curse Prometheus.
I could see concrete evidence of the inclinations of each. For my Athenian friend was well provided with handsome slave-boys and all of his servants were. pretty well beardless. They remained with him till the down first appeared on their faces, but, once any growth cast a shadow on their cheeks, they would be sent away to be stewards and overseers of his properties at Athens.
Charicles, however, had in attendance a large band of dancing girls and singing girls and all his house was as full of women as if it were the Thesmophoria, with not the slightest trace of male presence except that here and there could be seen an infant boy or a superannuated old cook whose age could give even the jealous no cause for suspicion. Well, these things were themselves, as I said, sufficient indications of the dispositions of both of them.
So, given all these facts, were ancient people more bisexual than modern people? It seems like bisexual practices were far more common in those days than they are now.
The Etoro, or Edolo, are a tribe and ethnic group of the Southern Highlands Province of Papua New Guinea. Their territory comprises the southern slopes of Mt. Sisa, along the southern edge of the central mountain range of New Guinea, near the Papuan Plateau. They are well known among anthropologists because of ritual homosexual acts practised between the young boys and men of the tribe. The Etoro believe that young boys must ingest the semen of their elders daily from the age of 7 until they turn 17 to achieve adult male status and to properly mature and grow strong.
My knowledge is by no means extensive but it seems clear that sexuality nowadays should not be considered 'progressive' or 'progressed'. In truth, sexuality and opinions therein has always varied throughout history and it will continue to do so into the future. I wouldn't go as far as suggesting it's cyclical but it certainly evolves differently across culture and context.
IIRC the Athenians were quite partial to young boys and assisting them in becoming 'men'.
From what I've read, it does seem that the erastes (older partner) would usually be in his 20s, the eremenos (younger partner) would be maybe 15 or 16. It's not the extreme age differential we might have thought previously.
Also, it seems that not just Athens but across the ancient world it was very common to see a sort of general societal bisexuality, where chasing both women and "boys" (youths, lads etc... guys I think from about 15 up) was quite common. And chasing young men (early 20s) wasn't unusual either, see this poem from Maleager in the Greek anthology
Love in the night brought me under my mantle
the sweet dream of a softly‑laughing boy of eighteen,
still wearing the chlamys; and I,
pressing his tender flesh to my breast,
culled empty hopes. .
And reading Catallus, it seems that chasing boys was not an unusual activity for an ordinary Roman/Greek citizen. At least, I am certain (as you alluded to with your comment about progressiveness) that it was far more widespread than it is now for non-gay men
Funnily enough, the Papuan view came from an almost extreme form of misogyny (that semen = power, and women are attempting to suck your power out of you, so you should only give them some of your power for procreative purposes)