Think of the poem as more advisorial than judgemental toward a particular group - in this case, virgins/women. The poet is encouraging people to "seize the day" and not fritter one's time or life away being idle. The poet uses the analogy of the virgin's pursuit of marriage as a sort of call to action - to enjoy life, experience the religious and societal joys of marriage and most of all, not waste their time on earth.
Herrick, who was a priest, was simply expressing a philosophy which was popular during his day. The philosophy reflects an ancient theme the Romans called "Carpe Diem" or "Seize the Day". This idea encourages all people to live life to the fullest each day. The Roman poet Horace put it, "Let us eat, drink and be merry, for tomorrow we die." Herrick expresses the same thought in the first line of the poem when he writes, "Gather ye rosebuds while ye may." Since marriage was expected of all women, I don't think Herrick was forcing his ideas on women, simple expressing the common values of his day. In a time when life expectancy was short, his admonition that "the age is best which is the first" was probably fairly good advice.