Before starting out on any research into parish baptism records it is alwas worth remembering that a baptism entry is not the same as the birthday, and it is important not to confuse the two as whilst they can often be found close together, they may also be years apart.
A baptism will usually occur quite soon after the birth: a matter of days or weeks depending on the period involved and custom of the area.
However, if a child was sickly it may have been baptised privately at home, possibly by the midwife who was licensed to christen the child if needed. After its recovery the infant might be received into the church and this may be what is noted in the registers.
Occasionally families avoided the church, perhaps from conviction or a wish to avoid paying money but there might come a time that the church catches up with them, perhaps when the eldest daughter comes to marry.
That can be an instance when you might find indication of adult baptisms or a group of children being baptised together at a much later age than usual.
Although Nonconformists had to marry according to the rights of the established church from 1754, they certainly did not have to get their children baptised and you might well have to look much further a field.