No, I don't think a 16 week old should be neutered. I like to wait for the growth plates to close before neutering. I got Jackson fixed at 7 months old and I personally believe that's a pretty good age for a small dog. If I had a large breed, I'd probably wait for as long as I could. I strongly believe in neutering but I also don't agree with early spay/neuters.
I do think neutering earlier helps prevent marking issues. But I don't personally think your pup is 'marking' -- it sounds like he's simply not potty trained. He never will be potty trained if he's continued to be given free roam of the house, either. It's very important to ALWAYS keep your eye on him and keep him locked in a crate or an expen if your eyes cannot be on him like a hawk. Case in point: my dads female JRT mix was never properly potty trained and allowed free roam WAY too soon and she is now almost 4yrs old and has an accident every day almost. It's a pain the butt! Now they have just gotten to a point where they are lazy with her and it doesn't even seem worth it to start all over again (I personally would, though... lol. My dad is just lazy).
I'm with you -- the biting and rambunctiousness are all part of just being a pup! That changes with age and just maturing.
