I’ve switched all mine to vintage based on manufacture date, not registration date. Some councils seem to have totally varying ideas on when it should be done, but the statute mentioning ZV plate eligibility specifically states 30 years from manufacture.
It seems to be hit and miss. I was told that since Jan last year, it didn't make any difference when it was registered in the year, it was eligible for vintage tax from Jan 1 of that year. But I've seen posts where for some people that was not the case. As kdevitt says, it seems to be dependant on each county council.
All I can tell you is, a couple of years ago I tried to reclassify mine as vintage as date of manufacture, but my local tax office refused saying it was date of registration, despite their website saying otherwise.
It seems to be 30 years from date of manufacture, and all CoCo websites I've checked say so. The problem is none quote the relevant legislation that controls it, and to make matters worse the RSA website says a vehicle becomes vintage after 30y from first registration.
This is how vintage vehicles are defined in some other regulation (S.I. No. 281/2014)
"vintage vehicles” means historic vehicles, or vehicles of value to collectors, or vehicles intended for museums, for which a period of 30 years or more has elapsed since such vehicles were first registered and which are kept in a proper and environmentally sound manner, either ready for use or stripped into parts.
The left hand has no idea what the right one is doing.
The legislation unfortunately states '30 years of age', which is where the confusion seems to arise for the tax offices. As I mentioned above, the legislation on being eligible for ZV plates does state 30 years since manufacture - so its clearly the intention. I've never had a problem switching to vintage on anniversary of manufacture, and I'm in Dublin.
As someone else mentioned above - seems to be an increasing number of people who are doing the switchover on the year of manufacture only - so week one of the 30th year.