Haha he wants strength in his lower back. Resistance is gonna build strength, repetition isn’t the key. Besides if he’s never done deadlifts before his forearms strength is going to severely limit the amount of weight that ends up being “heavy” for him. That’s just my two cents.
Regardless of what you do Ilya , just make sure you’re form is perfect(especially with the back issues). I wouldn’t just start at it on your own, have someone who knows check your form, before you add any weight to the exercise. While good mornings are really simple, I’d still start off with maybe just a broom handle in place of a bar(or hammer), to get your muscles and joints used to the motion. Every bodies range of motion on them is different regardless because of flexibility. If you can watch yourself in a mirror while doing it, that’d be good for starting as well.