The article refers specifically to people aged 20-24 in 2016, but the headline just says "Millennials".

I, a millennial, was 30 by then.

My younger brother, a millennial, was only 23.

Millennials are people who were born between 1981 and 1996. Some millennials were having sex when other millennials were toddlers. I would call it poor reporting to call out a 15-year wide cohort when the research being reported spans a narrow 4 of those years.

That is an 8 year old article. Nearly half a generation ago. That article would how he comparing generation Z to older generations (assuming the focus was still on the average 20 something year old).