I once read a book about medieval life. It pointed out that with life spans so much shorter, everybody was a kid. When we read about lords and kings, we picture mature individuals (Richard Burton in "Camelot" is a good example.)

In the middle ages, people grew up fast and died young. We might picture Lord Arlen as 35, but the ballad writer was probably visualizing 19-year-old with raging hormones, little self control, and a few beers in him.

The English nobility had an unusual tradition for the time - they let their daughters get as old as 20 before they married them off. Other people married them off at 14 or so. Depending on where exactly the lady came from, she could have been just a kid by our standards. No wonder the wasn't cagey.