It's not a wild exaggeration and it's possible for most (healthy) middle-aged men within a year (usually a lot less), except for the truly unendowed. (We don't control our genetics and/or other ailments, but I think it's better as a policy to not try to rank yourself in this regard and just be Pollyannaish about it and assume you can achieve it.)

5x5 deadlifts is generally too much volume and probably constitutes overtraining for you if they're sufficiently heavy. Admittedly, when you're not particularly strong it's less stress and more recoverable (because they can't be that heavy).

Not being able to deadlift 405 after three years is generally indicative of poor programming (if you're trying to get stronger, at least) and/or poor recovery. You have to eat, you have to sleep, and you have to increase the weight each time.

If you're an adult male who's been training consistently for 3 years and can't deadlift 405 for a working set, you probably need to change your programming.

Being 40 isn't really an excuse. You're 40, not 80.

Try looking into 5/3/1, Hepburn style programming, or Tactical Barbell.

If those 30 seconds are the total time the bar is in your hands and off the floor it sounds reasonable tho, doesn’t it? The numbers quoted match about what I personally experienced

Yeah, I was doing 5x5 forever. It is a good starter, but you will plateau.

Everyone will have their own methods here, but after years of having marginal growth per year I changed it up.

I now only do 1 set per exercise, 3-4 exercises per day. For arm focused exercises I do 15 reps in 1 set. For everything else, I do 20 reps for a set.

If I succeed, then I up the weight for the next exercise (2.5lbs for arms, 5lbs for everything else).

If I fail, I do a drop set and shave off 20% per set taking just 30 seconds per drop.

I use the drop set as both the thing to help the growth, and the thing to punish me for failing to increase the initial set. If I get my 20 reps, I get to move on, so I push really hard because the drop set totally sucks.

If I fail 3 weeks in a row, I drop the weight.

Been doing this for the last two years and I am 47, and each year I have increased my strength by 20-40% depending on the exercise.

I also keep the number of exercises per day to be minimal. With 5 days in the week, I do just 3-4 exercises per day. M, W, R are 1-2 from the 5x5 program (squats, deadlifts, bench, should-to-overhead, rows) along with some extras that I want to focus on. Tues, Thur are more extras, and ones that I am willing to sacrifice if I have a busy week. This means I can still hit the gym just 3 days a week, and hit the core exercises. Also, the core exercises are rough, so Tue/Thur are almost like easy days.

Here is my schedule:

M: Bench, 20degree lying dumbell curl, Squat

Tues: Lat Raises, Hip Thrusts, Neck exercises (put a plate on your head and do lifts from 4 different angles while lying down)

Wed: Overhead press, Deadlift, Cable Row

Thur: Tricep Rope Kettlebell swing Lat Pull down

Fri: Dumbbell Bench Dumbbell Shoulder Barbell Row Front Squat

You'll notice their are some repeats in there with cables and dumbbells. This is helps hit the muscle groups twice a week, but with some variation and some different stabilization. I chart all this in a google spreadsheet with each column being a week so I can see my progress, and so I can see if I missed anything from the core days in the week, and I happily change up days so I ALWAYS hit the core 3 day exercises.