My class 1 medical expired in Dec 2013. I was thinking about renewing it this month, but will not be flying until May 2014 ; would it be acceptable to renew the medical in May without any problems?
The very simple answer to that question is : "YES"
Postponing the renewal of a Class 1 is no problem at all, so long as you are not exercising class 1 privileges. At your age your existing certificate remains valid for class 2 privileges. You seem to be considering a delay of just a few weeks ; the worst problem can come when a class 1 is allowed to lapse for much longer periods (eg more than 5 years since issue). There is then a real risk of finding yourself having to go back to Gatwick for another Initial Class 1.
If you need the "full monty" this time ( routine plus ECG plus audio), it would be wise to start saving now !