I REALLY debated this with my DD. Her birthday is the 29th Aug so she is the youngest in the school. I talked to several of her nursery workers and asked if THEY thought she was ok going full time or if i should put her in part time - they all agreed that she was more than ready to go to school and although she is the youngest she is by no means 'behind' anyone else (this has since also been told and proven to me by her teacher who says she is one of the most independent, strong minded and friendly child in the class.)
I also spoke to my best friend (who works in childcare) and she says that going part time can actually delay your child and can, to some extent, exclude your child. For example if your child is in the minority (or the only one) who is going part time then their friends may form a tighter bond to other children who are there ALL the time. They also 'miss out' on some of the learning and playing and so can find themselves behind in certain things purely because there were not there when the rest of the class was taught it.
At the end of the day it is YOUR decision and only you can decide if your son is ready or not but why not talk to his nursery/pre school teachers if he has any and see what they say? Its hard not to compare your child to another of a similar age but tbh they change SO much when they start school and already Mills has come on leaps and bounds with her reading, writing, spelling & maths and she has only been there 6 months. I hope at least some of this helped. xx
EDIT: Only 2 out of Mills class of 30 applied for part time and by the end of the first week they both decided to take the leap and start them full time xx