I never realised that the age of diesel had an effect. We don’t use our narrowboat that often unfortunately, so I know our diesel is a mixture of old and new. Some will be more than 12 months old. Can’t say I have noticed any issues. As for alternatives. Electric : great but would constantly need somewhere to recharge.
Petrol : I’d rather carry diesel than petrol for safety reasons.
Is the age of diesel really an issue?