Dear S.,
Here is a list of some milestones that 4 year olds should be reaching. Not all kids are the same, I wouldn't panic. I would consider providing a "print rich" home environment as another person commented. I would also provide teachable moments. Boys may not be all into sitting and writing letters (though asking them to do so isn't an all bad idea) however, it may be more fun to write letters w/ him in his sandbox or get some shaving cream and let him play with it, and also write letters/numbers in that.
The scribbling thing isn't that big of a deal, as long as his grip on the crayon, marker, whatever is the same as it should be for a 4 year old. Look up "Pencil grip" on google and see if your son holds the pencil correctly as that is something that is a fine motor skill and also impacts future handwriting and the such.
I wouldn't stress about it, just keep an eye on it and definitely find ways to incorporate learning into play. A book or two from a teacher store might give you some really good ideas!
Milestones: 4-Year-Olds
Motor Development: Gross Motor Skills
* running is more controlled; can start, stop, and turn
* turns somersaults; hops on one foot; gallops
* can easily catch, throw, and bounce a ball
* can brush teeth, comb hair, wash, and dress with little assistance
Motor Development: Fine Motor Skills
* copies crosses and squares
* prints some letters
* uses table utensils skillfully
* cuts on a line
Language and Thinking Development
* uses a 1,500-word vocabulary; speaks in relatively complex sentences ("Mommy opened the door and the dog ran out.")
* understands words that relate one idea to another - if, why, when
* continues to learn through experience and the senses
* understands, mostly, the difference between fantasy and reality
* understands number and space concepts - more, less, bigger, in, under, behind
* thinks literally; starting to develop logical thinking
* begins to grasp that pictures and symbols can represent real objects
* starts to recognize patterns among objects - round things, soft things, animals
* grasps the concepts of past, present, and future but does not understand the duration of time
Social and Emotional Development
* takes turns, shares, and cooperates
* expresses anger verbally rather than physically
* can feel jealousy
* may sometimes lie to protect herself, but understands the concept of lying
* enjoys pretending and has a vivid imagination