Here is Bram Steijn‘s second blog post for the MA course Testing Prescriptivism:
I was sitting in the train, checking my Facebook messages, when I stumbled upon the following mistake in someone’s profile text: “living life at full”. The person in question wasn’t a native English speaker, so I let him off (as you do as a student enrolled in a course like “Testing Prescriptivism”). Instead, I internally corrected the sentence to “living life to the fullest” and put the case to rest.
However, the second I did so, I started questioning my correction. Can something be fuller than full? Surely it cannot. Suddenly, “living life to the fullest” sounded odd. Yet the alterative, “living life to the full”, felt even more out of keeping. Which version was correct? As someone who holds a BA in English literature and language – and is currently pursuing his MA – I felt horribly incompetent when I realised that I could not answer this clearly simple question with a certain resoluteness and authority. I also did not have my copy of Oliver Kamm’s usage guide with me at the time I spotted the mistake, so I could not consult his wisdom either. A quick search in Google nGram revealed that in the English language “living life to the fullest” became significantly more popular than its “living life to the full” counterpart after the year 1983.
Based on this, it seemed that “living life to the fullest” was the way forward. So just when I thought I had found the answer, the train stopped at some station and an advertisement like the one below came into sight: “taste life to the full”. It was now no longer just a minor annoyance.
As soon as I got home, I turned to my volume of Oliver Kamm’s usage guide. While there was no entry dedicated to “full vs. fullest”, there was a section on absolute adjectives. Kamm mentions that language pedants are of the opinion that absolute adjectives such as peerless, matchless, eternal, and also full, “cannot have superlatives” (Kamm 2015: 147). Kamm believes differently and remarks that “you can go right ahead and use comparatives, superlatives and intensifiers with absolute adjectives; the best writes do” (Kamm 2015: 148).
Even though I now had my answer, I decided to consult the British National Corpus and the Corpus of Contemporary American English to find out which version was more popular among users of the English language. The results from the BNC are overwhelmingly in favour of “life to the full” (49 hits vs. 3 for “life to the fullest”). The situation is reversed when we look at COCA. Not only is “life to the full” recorded less frequently than “life to the fullest”, the corpus also shows that the former is in decline, whereas the frequency for the latter is steadily increasing. After I discovered that Google nGram can differentiate between British and American English, I queried it again. The results are striking (you can find out exactly how striking, by setting the language in the box below the query box to either British or American English).
I decided to put these results to the test and ask both a Brit and an American to finish the following sentence: “Living life to the …”. The results, while by no means scientific, were entertaining. My American classmate (thank you, Madeleine) immediately finished my sentence by saying “fullest”. My British and Scottish friends, however, did the same! Both went for “fullest” over “full”.
Having given this topic more thought that it probably deserves, I have decided that even the initial ‘mistake’ I spotted was altogether fine. After all, I knew what the person in question meant. He thus communicated perfectly with me and, in all likelihood, with everybody else who read it. Besides, Milton employed a similar construction in his writing when he wrote: “[h]is Regal State Put forth at full” (OED) – a construction which, although obsolete now, was considered legitimate at the time Milton was writing his epic Paradise Lost. Personally, I can see the point that a glass cannot be fuller than full, and that one encounter cannot be more fatal than the next, but if you are only living life to the full, then you simply are not trying hard enough!
Bridging the Unbridgeable 
For me, as a native BrE speaker, ‘living life to the full’ is natural. But did the original speaker mean ‘living life at full speed’? Or perhaps that’s just what influenced the original unusual construction.
The “Longman Dictionary of Contemporary English” (1978, first edition) has: “to the full: to the greatest degree; very greatly: We enjoyed our holiday to the full”, with the entry under “full n”. The 1987 second edition had something similar. The 1995 third edition again had something similar, except that it had now moved under the “adj” entry, with the “n” entry being deleted. The 2003 fourth edition then had: “to the full; to the fullest AmE”, with the entry still under “adj”, though the “n” entry had now been restored. Presumably it couldn’t be listed under “n” unless “fullest” could also be a noun? Meanwhile, the 2009 fifth edition, which is the last one I have, has “to the full (also to the fullest AmE)”, again under the “adj” entry, but again with the “n” entry now restored.
It seems that “to the fullest” is clearly American, whereas “to the full” is British. I do think that it is interesting that both my British friends answered with “fullest” rather than “full” (no hesitation in either of them — not even after I told them why I asked the question). Perhaps it has something to do with where they live (north of England and Scotland) or their age. I could be wrong, of course! It could also be that “to the full” is slowly losing ground. I honestly do not know!
I am sure that the original speaker meant to say “living life to the full/fullest”