> The usual marriage age for a girl in premodern western European culture (and many other cultures worldwide) was "the onset of menses," or about 12 to 14 years old.
The wikipedia article [1] doesn't agree with you. It suggests marriage in the mid twenties was most common, although there was regional variation. Noblewomen, such as the fictional Juliet, married younger.
[1] https://en.wikipedia.org/wiki/Western_European_marriage_patt...