Just to add to everyone else - I have 4 boys and none of them went to nursery/pre school until a year before starting reception class. In fact, ds3 didn't go at all, just started in reception (reasons were - the schools were changing from 3 tier to 2 tier, ours was closing and they were moving to a new school at the Easter, we were planning on moving area so would be changing schools later, and it wasn't vital for him to go anyway.)
With the changes he could have ended up in 3 different nurseries in one year, not something we wanted to do to him.
In fact, that year we moved in the July and chose to 'otherwise educate', aka home school, ds2 for the last two weeks of the school year (ds4 was nearly one so not in school) so in reality he got an 8.5 week summer holiday. He was chuffed! The new school was failing ds1 (since been diagnosed with aspergers) anyway, so had pulled him out and was home educating him for a few months already, so felt justified not putting ds3 in their nursery before we moved.
The 3 oldest started at a nice village school the following September and ds4 did go to their pre-school the year before starting reception.
They all 'socialised' in toddler groups etc and could all count/identify letters, get dressed, use cutlery, say please and thank you etc before starting school so were not 'behind' children who had been to nursery from 6 months old.
It's probably a good idea to make sure your son is used to being around groups of children before he starts school, makes the transition a bit easier, but you have toddler groups to go to and are planning on putting him into nursery at 18 months anyway, but it is not necessary if you don't want to use nursery.