Head? You mean full body right? The head is the person

Cryogenic pauses on time spent do not count as years lived.

Does this resolve YES if someone, say, lives 80 years, goes into cryonics because of a disease with no known cure, gets revived in a few centuries, and lives another 70 years?

@April Yes, I would resolve that affirmatively. Although, the spirit of the question was in one continued lifespan, better gaging the development of medical technology in the next 150 years than that of centuries from now.

Fair. However, consider “grow your own organs,” advances in CRISPR technology possible, and the rapid rate of medical knowledge historically.

It would take some serious genetic advances to pull that off:

"A human cell can divide roughly 50 times before it dies out. It's called the Hayflick limit, and it's become a real headache for the anti-aging science. As long as the limit holds, it suggests a maximum human lifespan of 120 years" - Link

And I personally doubt we'll ever quite pull that off. This wouldn't be simple genetic engineering but advanced to a point where we would have to completely alter even our telomeres and that's still a long way off but we are making some progress:

https://med.stanford.edu/news/all-news/2015/01/telomere-extension-turns-back-aging-clock-in-cultured-cells.html

Telomere extension turns back aging clock in cultured human cells, study finds

Researchers delivered a modified RNA that encodes a telomere-extending protein to cultured human cells. Cell proliferation capacity was dramatically increased, yielding large numbers of cells for study.

Lifespan is challenging to predict as many influences need to be considered, such as genetics, environment, lifestyle, healthcare, socioeconomic factors, social support, mental health, gender, and medical and/or technological advances over time, ... However, when we analyse the differences over the years we can see that humans are close to having reached the natural limit. For further big increases, a big lap in medical or technological advances would be needed.

@Alice24a9 I will bet on a yes, and proceed by saying:

If we follow a certain protocol of do's and don'ts it is eventually possible. I will on the other hand also point out the fact that those born during these eras have been exposed to different lifestyles, both health and unhealth. There is a possibility of educating and promoting a certain lifestyle that will encourage people to focus on healthy nutrition and more exercise which leads to extension of life span. Come to think of it, if we could eradicate the diseases that shorten the life span of humans like cancer, heart disease and other hazards, it would prolong the journey. However, these are not always curable diseases but when detected on time they can be minimized or even cured, with the help of all the necessary technology we have, and this will highly increase the duration of life on earth. Having said all this, yes, I believe to reach or go above pass 100 years of existence on this earth if we follow this steps and protocol. Good nutrition, Exercise and Peace of Mind (Less or No stress at all). It is possible for those born in the 1990 and 2000 to live longer.