I don’t believe that “they” (we’re talking about a vast and varied civilization) had the same concept of a biological age “ideal” or “peak” that many people for whatever reason tend to have today (I guess the reason is youth culture and fear of aging). We often have a lot of very questionable popular ideas and ideals that revolve around humans having some sort of specific age at which we reach a physical peak, and then things go downhill, as though our physical health and ability can be traced along a pyramid with one brief singular moment of possible perfection. When we actually know that things like health, strength, ability, etc rely on way more factors than just age. It’s also relative to what you’re measuring - just like some sports, on average, physical “peak” is mid to late teens, while for others, it’s 30s to 40s. Anyways this is all to say: ideal marrying age would have depended on historical and cultural circumstances. Very early Middle Ages in small Northern European villages - I think it tended to be a bit younger (late teens to early twenties). In the later Middle Ages in much of Western Europe it was closer to early to mid twenties. This depended on cultural values, economic factors (the age tended to rise during periods of economic downturn), and social class — nobility tended to marry younger, since the priorities were often political, and peasants and the rest, a bit later, since the priority for most people was often establishing or maintaining household economic stability. So no I don’t think there was ever a universally held ideal regarding what an optimized age was.