Microchipping of dogs becomes compulsory in England form April 6th, 2016. Your dog must be chipped and registered on an approved database within 21 days of that date, and you also have 21 days to change details (e.g. address, telephone number on the database. It is an owner’s responsibility to make sure that these details are kept up to date.
If your dog is elderly it is not exempt from being microchipped unless your vet provides a certificate stating that he or she cannot be microchipped for health reasons.
So if your oldie is not chipped, make an appointment to have him chipped or see your vet if you think he should be exempt, before April 4th.