In Mary and Joseph’s culture it was. In our culture it would be a substantial problem.
Children are expected to remain children until a much later age. Even when I was a kid, people married around 18 to 21, at least in this part of the country, and no, I don’t live in the mountains, because the mountains are a good 15 minutes away. I realized, even as a confused, liberal Catholic back then, that our culture was out of step with nature, and the demand that people had to have a high school education in our society was a sure ticket to immorality. Sure enough, the attitude progressed, through the necessity of college, and beyond.
But back to the topic, and I’m just thinking that the 17 year old might be a really great kid, perhaps a frequent mass attendant, and a saint in the making, whereas, a boatload of guys of the same age might be interested in one thing, instead of the three things, in their correct order.