He is not sweet, he is a Lab and he's waiting for you to turn your back, so that he can turn into a little furry piranha and see how you taste.
You will have to socialize him with lots of people, and after shots with lots of dogs. But for now, you need to teach him Bite inhibition, see the Sticky: The Bite Stops Here.
Get him a Kong and a hard rubber bone to chew. Labs need to chew. They also like to swim, and play with their water, and drink from the faucet.
And start training him.... 4 weeks ago

He can learn anything you can teach him... Mine knows how to count and how to read !
See:
http://www.dogstardaily.com/free-downloads
Tweaks to Bite Inhibition - I just posted this for someone else... (Sticky:The Bite Stops Here ... Using Ouch or Yelp!)
1. When the pup bites, then yelp. It should sound about like what the pup does when you step on its paw...don't step on her paw for a sample

. When you yelp, the pup should startle briefly and stop nipping. Praise and pet. SHe'll bite again.
2. When she bites the second time, Yelp. When she stops, praise and pet. SHe'll nip again, although it may be a little gentler. ...
3. When she bites a third time, Yelp (see a pattern?). But this time, turn your back for 15 - 30 secs. If she comes around and play bows or barks, then that is an apology. Accept it, (This is important) praise and pet... and cringe in expectation of the next nip...
4. When she bites the 4th time, Yelp, then leave the area, placing her in a 2 min. time-out. It is better if you can leave, rather than moving her. Then, return and interact. (SHe's still hungry...)
5. When she nips the fifth time, yelp, and leave the area, stopping interaction for now.
Immediately after you yelp (in this case), you should notice that the second nip is a bit gentler... not enough, but a bit.
Dogs need to sleep over night in order to learn their lessons. So, keep doing this for 3 days. By the third day, you should notice significant Bite Inhibition. SHe may still nip, but it will be softer and she won't draw blood. Keep up the training and make sure that everyone yelps.... Very powerful method.
If you learn the technique, then you can apply the "yelp" to other circumstances, also. I believe that "yelp" is "Please don't do that, I don't like it." in dog communication. For example, I used the Yelp method to shape an energetic Tug with very well-defined rules, yelping when my dog broke the rules.