When a young rattie hasn't been handled from birth, it can take them a good week or two to get used to their new people. Handling can be almost impossible until they learn to trust you. Often having a treat in your hand for them (Cheerios is a good choice) will make the hand seem less threatening, and by the end of the week they'll be looking forward to that visit from the hand-- and may even want to climb on it. Here's a link to some good articles on rattie trust training and getting acquainted:

Trust Training

Getting Acquainted with Your New Rats

Handling Your Rat

I would also recommend getting your rat a cagemate (introductions will be especially easy if there is a same-gender littermate still available where you found your rattie). Rats are very social creatures by nature, and this will give your little guy a friend when you aren't around to play.