He is not ready.. Why would he need to write?
Maybe just have him trace the letters with his fingers.. then see if he is interested in trying to copy the letters. But do not get upset with him if he is not interested,
He would enjoy some fine motor skill activities to build up some of those skills, he will not realize it is therapy or exercise.
With playdo, have him make tiny balls with just his fore finger and thumb. Then have him place them in a line, side by side. After they are all lined up, have him squish each one with his forefinger or thumb.
Get a big piece of paper and have him draw some straight lines. then some wiggle lines. Get a small car and have him "drive" the car with just his fore finger then just with his thumb and have him "drive on the lines."..
Pour out a piggy bank and have him separate all of the coins into piles. Then have him place each coin back in the bank.
give him a pair of tongs and have him practice picking up different hings, only using the tongs.
Then let him try with a clothes pin..
Paint brush with water "painting" on a sidewalk
using pencils to connect some dots..
These are all things that will help strengthen his fingers and hands. They are all fun..
I just remembered these also..
I forgot about these.. Have him button every shirt you hang up as the come out of the washer or dryer once they are hung up.
Get a box of large paper clips and have hm make a chain.. Then later get a box or small paper clips and have him make those into a chain.
Hang the chain in his room at his level.. Each time he makes a picture at school or home.. have him "attach" it to the chain.
Give him old magazines and have him cut out pictures. Then give him glue sticks and to Paste (with a brush applicator) and let him make collages.. The next time you need a gift wrapped. Consider letting him cover the box in cut up pieces of paper, news paper, etc..
REMIND him, "we NEVER" cut up books.. And only the magazines and newspapers mom, dad and the teacher allow you to lose.