I highly recommend a corn.
I'm a beginner snake owner and I chose corns for their temperament and looks. They have so many beautiful variety of morphs out there, it was hard choosing the one I wanted most! Note, that I have an immense and irrational fear of being bit by anything. Having had my boy for roughly over two weeks, I have to say, he has been a joy to handle. Personally, I like having a snake that I can watch and is active. Just this afternoon, I walked into the gecko room and there he was exploring the top of the cage. I think that would keep a seven year old's interest. They're easy maintenance, too. It's really fun to look for him and find his little face peeking through a whole in the aspen bedding.
I would consider a Ball Python or Rosy Boa, if I were to look into getting into another species. The latter however, is known to be bite happy, but they are pretty to look at.