This is how I would look at it.
NR 1: Mane at cheeks and mohawk still pretty distinct and no mane at all yet between mohawk and ears and thus < 4 years.
His nose is quite pink, but a bit more difficult to assess, but from what I can see could be 3-5 years.
Teeth not visible.
Lower jaw not sagged so definitely not an old lion.
In general the fur looks quite glossy indicating a younger age, he has some scars but that could be from fighting over food.
The face looks quite small, definitely not a huge prime age male lion. I would say he's about 3 years old.
NR2: Mane in the neck is longer than on cheeks and mohawk (more difficult to tell on cheeks than top of head where the mohawk is), which indicates about 2-3 years old.
Difficult to asses his nose, but I see a good amount of pink, could be anything from 2-5 years old.
Fur looks nice and shiny, indicating a young age (the whiskerspots are still very clear). There are some scars on his face, but again, could be from fighting over food (versus territorial fights) and those scars look fresh, and the visible ear is intact.
Can't see the teeth.
Head doesn't look huge.
I would say this male is 2-3 years old, but younger than the first male, and most definitely not an old male.
NR3: Not much I can say about that from this picture. The mane hasn't filled in on his shoulder indicating he's younger than 5 years. It looks like there are dark marking at the back of his back legs which develop in males who frequently mark their territory so he's probably holding tenure over a pride. In general those markings are more conspicious early in the reproductive career, but it's hard to use it for age estimates, as it could be anything from 3-7 years.
His fur looks to be in good condition.
The general feel for me is is that this male is a bit older than the previous two, about 4-5 years old, but definitely not an old male.
So I would say they're all pretty young, none of them at prime age yet. But all of them would be physically capable of reproducing, and all of them would be strong enough to dominate a female to mate with her.