Yes, a 5'11" boy would be considered tall compared to his girlfriend who is 5'1". There is a significant height difference of 10 inches between the two individuals. In many cases, such a height difference can be noticeable and may draw attention, but it's essential to remember that height differences are entirely normal and vary among couples. Ultimately, what matters most in a relationship is compatibility, love, and mutual respect, not the height difference between partners.