Granted, but I guess I was a little unclear. I was talking about what was considered desirable in a potential mate, not specifically about actual marriage. Even if men normally married women who were less than a decade their junior, it was still the tendency to be drawn to younger women. And sexual fantasies or fictional romantic scenarios are often exaggerated, so works of fiction presenting 18- or 19-year-old women as the peak of desirability would not have been uncommon.
Also, we're not talking about "much older men," but about a man in his early to mid-30s like Pike or Kirk being interested in a woman who's 18 or 19, a gap of only about 15 years. (Yes, Pike has been retconned now to have been in his upper 40s or so as of "The Cage," based on Bruce Greenwood's and Anson Mount's ages, but Jeffrey Hunter was in his upper 30s when it was made, and Roddenberry intended Pike to be c. 34.)