Answer:
There are two answers to that. One is that they weren't, because of their actions and sudden bursts of love, anger, and sadness. On the other hand, however, marrying young was often the norm, and they couldn't have been the only people to be in that kind of situation. I think that, comparatively, they were more mature than some of the other characters in the story, such as Marcutio, and, depending on how you look at it, the heads of both families themselves. That is why I'd say that yes, they are mature enough, in that time period, for a relationship and marriage.
Step-by-step explanation: