> It's better if you can write something like: "If you were born before 6 April 1960 ... otherwise ...". Note that "after 6 Apr 1960" is arguably more ambiguous than "before 6 Apr 1960" because there's a slight risk that someone could interpret "6 Apr 1960" as meaning 1960-04-06 00:00:00.
I strongly prefer pairing “before” and “on or after” (or “on or before” with “after”) when it comes to dates. “On <date>” is widely and conventionally understood to encompass the entire day, and it seems to make it far less likely than with after/before alone with “otherwise” that people will trip up over boundary conditions. But the right phrasing is highly sensitive to the context and the underlying rule; if it's an age based rule and you have fixed text that doesn't dynamically adjust by dates you can't use date-based language even if it would be clearer.
I strongly prefer pairing “before” and “on or after” (or “on or before” with “after”) when it comes to dates. “On <date>” is widely and conventionally understood to encompass the entire day, and it seems to make it far less likely than with after/before alone with “otherwise” that people will trip up over boundary conditions. But the right phrasing is highly sensitive to the context and the underlying rule; if it's an age based rule and you have fixed text that doesn't dynamically adjust by dates you can't use date-based language even if it would be clearer.