Millennial is generally born 1980 and on (the name comes from the fact they matured into adulthood around or after the millennium). Ages 0-39 by that metric, and actually it's already freaky that you could call a 39 year old a millennial.
Gen-Z is the generation before them, born about 1960-1979. They're mostly not the but of the joke just yet, but it'll just take time. Ages 40-59
And Baby Boomers or 'boomers' as they're popularly called especially when dismissing them were before then. Ages 60-79.
I'm not sure sure where Generation X fits in with that. I thought they came in between boomers and Gen-Z. And that leads to the question about what happened to Gen Y?
I've not looked at that the sun link, because it's a rag owed by Murdoch (Rupert, not the one from the A-Team), and while he doesn't own Fox any more, I'd still rather not support his business model.