Returning Lifter Question

As an over 35 lifter (42), I’m wondering how much cardio is good for my program, and how much might just impair it. After lurking around for months here and reading some of the posts, I’m trying out some of the workouts I see on this site. I recently started back (from 12 yrs), and these are all new to me.

Time is an issue, so I’d like to get in and out quick. Question is, can I do this HIIT a few times a week with, say, a Waterbury full body 3-day-a week plan, a Staley EDT plan, or what? (The Staley plan looks like HIIT to me.) Is it going to have negative effects? I guess the question is will it affect muscle gain, nervous system, etc.? I’m in pretty good shape, and probably want to do some kind of a full body workout as it’s easier for me.

When I lifted before, I never really did cardio, but, as we get older, we need to. Tried the HIIT this morning on a stationary bike for 12 mins, 20 secs on and 20 secs off…brutal.

Been hunting around for an answer somewhere on this site, but can’t seem to find one.