Age has nothing to do with food aggression.
Where did you get your puppy from? If you adopted it from a shelter, maybe your puppy had a bad up bringing and was never taught how to and how not to act. Or maybe it was a stray and had to fight for its food and doesn't know any better now.
First off, I'd make sure no one comes near his food while he's eating until you have his food aggression under control to make sure he doesn't do any damage to anyone (person or animal.)

NILF works for a lot of people. (nothing in life is free)
http://www.dogo.org/Education/NILF.htm

You need to make sure your dog knows that YOU are in 100% control.

As for him attacking people when they scare him... why would people be scaring him? Are they doing intentionally if not, when does it happen?
As far a separation anxiety... I have a dog that suffers from it and I cured her by adopting another dog to keep her company, and it's done wonders for her! I realize that not everyone can just run out and adopt a 2nd dog.
*Some things you can try are:
*Leaving a TV or radio on while you are gone.
*Giving your dog something that smells like you to sleep on while you're gone.
*Make SURE not to make a bid deal when you leave, don't pick him up... kiss all over him.. etc... as you're walking out the door.
*Toys, stuffed animals, things to play with and chew on
*Stuff a Kong with peanut butter and treats to keep the dog occupied.
http://www.drsfostersmith.com/produc...&Ntt=kong&Np=1
*There are also plug in's that you can use that releases a calming pheromone.
http://www.drsfostersmith.com/produc...fm?pcatid=8906
*Do you have a crate for your puppy? Crates are GREAT for dogs with Separation. If you don't already have one, I HIGHLY suggest getting one and slowly introduce your puppy to it.

I hope something I said can help you out!
Here are some websites for you to look at:
http://www.usask.ca/wcvm/herdmed/app...s/anxiety.html
http://www.hsus.org/pets/pet_care/ou...n_anxiety.html
http://www.wagntrain.com/SeparationAnx.htm