My daughter, who will be 3 in January, did this for quite some time. Now she has advanced to throwing toys and pushing people. Is he very verbal? The pediatrician told us this behavior tends to lessen as they begin to be able to express their frustration, excitement, etc. through words better. I wish I had an answer other than that as I'm pretty tired of issuing time outs, time ins, power sitting, suspending privileges, taking favored toys, teaching simple coping methods, etc. None of it seems to have a long term effect although there is consistently a consequence for those actions in this house.
As far as it being a boy thing, I think it has nothing to do with being male or female - my oldest daughter never did this and my son hasn't come into this age group yet but definitely has a very different personality than his aggressive sister.
Being possessive is definitely a stage I've seen with all my kids, both foster and adopted, and a long lasting one at that. As someone else suggested, teach him how to share, even if only at short intervals. Don't argue that something is not his - he won't fully understand that at his age.
Best of luck,
K.