People, say, 60 years old and older.

Пенсионеры до 80 ?
http://calbooming.sdsu.edu/documents/TheThirdAge.pdf

Grumbler, it says 80+ (plus)

yes, but this stupid (in this context) notation doesn't mean any age above 80.
"The Third Age is now considered by many to be the “golden years” of adulthood. It is generally defined as the span of time between retirement and the beginning of age-imposed physical, emotional, and cognitive limitations, ..."

The author equally could say 66+, 75+ etc.
"approx. early 80s" ?

That means usually between 60 and 80, but it can extend beyond 80.

есть немного другие термины
60–75 лет – пожилой возраст, так называемая ранняя старость
75–90 лет – преклонный возраст, так называемая поздняя старость
90+ – старческий возраст, так называемое долгожительство

https://ru.wikipedia.org/wiki/Старость#Понятие_«третьего_возраста»

With proper refrigeration, fresh flowers will keep for 2 to 3+ days. (=definitely 2-3 days, but maybe more)

I don’t understand your argument. The article is very plain and the notation makes perfect sense to me.

Yes, I understand this, but my technical background doesn't accept this notation.
Neither it accepts very common, say, "from 10 - 15", i.e. when a hyphen is used instead of "to/till" (it's fine, but without 'from')

Gotcha!