Another comment about age (I'll be 70 in a few weeks)

I wasn't sure what group this was targeted to. For example, the cautions you mention - I was in a 3x weekly aerobics class right up until the pandemic, and 5 of us were over 65. We all did, with no difficulty and much benefit:

Squats with dumbbells (I do goblet squats with kettlebells, one of my favorite exercises)

Leg Press

Upright Rows

Deadlifts (I do Romanian deadlifts with Kettlebells)

HIIT

Our teacher said the oldest person she had had in class was 77, and he did all of the above with a great deal of energy.

I'm not saying everyone can do this - there are a lot of 20 year olds who never exercise who might require a lot of prep to do it. In fact, up until 2 years ago, I was doing psych evaluations with teens. Once in a while I'd get someone on a school team who admitted he was too lazy to do the recommended workouts. I'd say, "you want to get inspired to workout more? " Then I'd challenge them to a pushup competition. Since I could be reasonably confident none of them could do 50 consecutive pushups, I'd always win, and they'd say, "Wow, I gotta go home right now and start working out!)

So if that was all too long:

1. Please clarify what age group you're talking about (60-100, 70-90, 80-100?)

2. Can you say something about the research you used for the exercises you say elders shouldn't be doing? I'm particularly curious about HIIT, as I love doing it, and quite a few seniors at the local Y swear by it.