There is definitely a difference between apparent age and actual age. Some people 'look young' or 'look old.'
With elves, we generally want older actors (not older than 40, but not teens) who 'look young'. That allows them to appear somewhat ageless. If you cast an 18 year old, you're going to notice that person 'looking older' in a few years. Whereas a 30-year-old will not typically look too different at 35. Almost everyone looks older when you put pictures side-by-side of them 10 years apart - that's mostly unavoidable, and you rely on the audience not binging/watching seasons out of order to make it work. I have noticed that TV shows often put less effort in trying to make someone look like themselves in an earlier season for flashbacks than films do - they expect you to use your imagination and go with it.
With Men, we have no need to keep them ageless - if anything, they are going to age faster on screen than in real life! With Beren - he is meant to look like he's lived through a harrowing time. So, while the character is in his young 30's...that doesn't necessarily mean the
actor would be. Because while some actors look like they've lived through a lot, more often they look quite pretty and would need some makeup to roughen them up a bit.
Here's the issue with apparent age.
That is Weird Al Yankovich at age 54. (He's now 60 years old.) Granted, he does not look like he's 20 in that photo; you can tell he's older. But he doesn't look
old, either. He could easily pass for a guy in his early 40's. (He is, by the by, a vegetarian - like Beren!)
Here is Alan Rickman as Severus Snape in
The Order of the Phoenix (2007)
Alan Rickman was 61 years old when this movie came out (he has since passed away). He is portraying a character who is meant to be the same age as Harry's father. While a 61 year old man
can have a teenage son...it's clear that Snape is meant to be younger than Alan Rickman. For some people, that probably works fine. For other viewers, it's probably a little disconcerting.
In contrast...here's a 50-year-old Keith Richards:
There is no denying that this dude looks like he's lived through some stuff. Now, in his case, it is almost definitely drugs (including cigarettes and alcohol). Beren's 'hard living' is more about being an outlaw living off the land and making his way solo through a land of giant spiders. That sort of thing. I am not suggesting that we need to find an actor with a coke habit to portray Beren! But, whoever we pick, should be someone who looks like he's lived through some stuff, and not be fresh-faced. Some wrinkles, some scars, some 'weathering' - any of that would be good. Some can be done with makeup, of course. But if the actor can't look a bit haunted to start with we probably can't sell the audience on what Beren has endured. If that means we have to cast an actor in his 40s to make it look like he's a 30-something who lived through some stuff...that's fine.