[HELP] Is this normal play or aggressive?

Hello everyone,Long time listener, first time caller. Firstly I'd like to apologise for any redditing faux pas or terrible formatting, I don't do much of this sort of thing.Here's our situation: Benny is a 1 year old mixed breed, he's a good boy and we love him so much, we got him at 6 months and have been very pleased with his temperament and behaviour, so much so that we decided to get him a playmate. Lily is a similar looking mix, at 5 months she's about half his size if that, and looks like she will stay quite small.Lily arrived 2 days ago and we introduced them at a park where they played a bit but weren't too interested in each other. We spent a lot of the first day out with them and they ignored each other mostly, but when we got home Benny just would not leave her alone. Obviously this is understandable because there's a stranger in his house, but he gets very hyperactive and relentlessly tries to play, his intentions are obviously good because there's lots of bowing, backing up to try to get her to chase etc. She plays a little bit and then starts snapping and baring teeth, he backs off for a second but then just keeps going back, nipping at her legs and neck. This happens for half an hour or so at a time. He stands over her a lot and mouths her neck too. Otherwise they seems to be getting on ok, he's growled at her a few times if she comes too near when he's on the sofa but she listens and goes off. They are quite happy to lay near even touching each other sometimes too which gives me hope that they are becoming friends?! I don't want to stop the play if it's healthy and I'm being over protective, but at the same time I want to intervene if things get too stressful for one of them. I don't want to scold Benny for wanting to play and I don't want her to feel bad for standing up for herself. We have been getting him to sit down and wait for a few seconds when he's really excited but he just goes right back in when we let him up. There's not been any yelps or whimpering during these times so I'm reluctant to start separating them. I've put her in her little fenced off area a few times when she seems tired of Bennys shit but she cries to come out again.I know it's very early days and we need to take time to get used to the new situation, I'd just like some reassurance that this behaviour is normal and will settle down soon enough, or if you think it sounds like there is something we could be doing better. We are very open to going to training classes for the both of them but it's not something we've booked in yet. Any advice or anecdotes if you've had a similar experience would be very much appreciated. This is our first time owning 2 dogs and I want to make sure I'm doing the best I can for both of them. Sorry if I've missed out anything important this was a bit stream of consciousness. Also I want to attach my dog tax but I don't know how to put a picture in because I am an actual dinosaur. via /r/dogs http://ift.tt/2slyDmK