Hope this will be somewhat reassuring. Both my sons are August born (15th and 31st) and neither had any interest in drawing or writing before starting school. Both were interested in reading and learned to read quickly and early.
DS1 is now 8 and in Y4, and his writing is still not his greatest strength, but it's joined up, it's legible and he can write quickly.
DS2, who turned 5 last August and is now in Y1, refused to pick up a pencil before starting school. Again, his writing is still not great, but he can now form all his letters correctly and produce legible (if large) writing.
It is very common among boys, and it is very common among bright boys, who may find that they 'know' how to do something and have no interest in taking the time to write it down - this is a problem in numeracy for DS2 who can tell me the answers in seconds, but finds recording slow and laborious.
I echo the suggestions about not doing writing per se at home, but finding other fine motor activities that your boy will enjoy. Both mine actually quite liked writing on chalk boards and small white boards. Finger painting or making patterns/letter shapes in foam, sand or rice is also supposed to be good, but that was too messy for me!
Lego and other construction toys, cutting (though mine both hate scissors too), threading or lacing cards, games like Uno where you have to organise your hand, tearing paper, kneading, rolling and cutting Play-Doh, are all good for developing fine motor skills.