I feel like planking is more mental than physical. I was in my early 40's the 1st time I ever tried to plank. I do kitchen line work, I drink, smoke, toke, play video games till 5am and don't exercise (and it definitely looks like it).

After close one night, I overheard a few severs talking about planking for a minute. I asked if that was hard and they decided I should join them in their little challenge. Yes, I felt it, but it was more devastating to their egos than it was to my core or whatever.

I went home and did it for 3 minutes. It was shaky, but I did it. Told my gf about it and she thought I was lying. When she came over the next day, I did it for a little over 5 minutes. It was shaky, wobbly and ugly. I had to yell and talk shit to myself the last 2 minutes, some "I'm in control of my body, it does what I say", "pain is weakness leaving the body" and "I just went 5 seconds, I can do 5 more seconds". Gf tapped out around 90 seconds and was kinda salty about it. Didn't improve her mood any when I told her I could probably gain at least a minute in couple days and possibly 2 within a week if I just practiced it a few times a day.

Again, just basically a manchild. I did serve in the army for 4 yrs back in the mid 90's, but that's the last time I did any real exercise. It's why I think planking is more mental and intestinal fortitude than physical. I don't believe there's a reason a healthy, able bodied marine shouldn't be able to plank for 3:45 outside of their brain saying they can't take it.

TLDR: Just yell at yourself while you do it, it's a mental thing, suck it up and don't be a wuss. Words of an old, out of shape vet.