I vaguely remember a quote from the Talmud, where a Rabbi was saying that in his youth the boys and girls would play together in the streets and there were no tzniut issues.
Does anyone recognize this and have a source?
You may be thinking of this similar passage in Talmud Bavli (BB 91b) with Sefaria trans.:
ואמר רבי יוחנן נהירנא כד הוו מטיילין טליא וטלייתא בשוקא כבר שית עשרה וכבר שב עשרה ולא הוו חטאן
And Rabbi Yoḥanan said: I remember when a boy and girl, of sixteen and seventeen years of age, would walk together in the market, and they would not sin
The Rashbam explains that "מטיילין" (walking) means "משחקין" (playing)