What is his age seriously?
SPOILER ahead: [spoil]If he was 25 to 30-years-old in average, during he’s on expedition to South America, should be his age was around 100+ today?[/spoil]
I need answers. 
I actually wondered the same thing, but then I realized it’s not really all that important.
It probably had something to do wirh [spoil]Kevin’s eggs[/spoil] as a fountain of youth. They had to cut that out of the film though because things were getting to bizzare.
Edited for spoiler content. – Mitch
quite logical. hmmm… 
He would have been around 20 when Carl was [spoil]at the movie theatre[/spoil], so by the end of the movie, he would have been in his 90’s, which is quite plausible. By the way people dressed back in the 1930’s or so, they would often appear, what we would think to look at least 25, by around 20. Adults dressed up practically every single day then…
- C-3PO
Edited for spoiler content. – Mitch
yeah…more logical answer. hmm…but i’m quite sure his age was in the middle of 20s or and the end of 20s. talk about successful adventures and incredible expedition back in the period of time.
Edited. There is no need to quote the entire post. – Mitch
My guess about Muntz’s age was that he was [spoil]about 25 years older than Carl - that would have made him 33 to Carl’s 8 at the beginning of the film, and 103 when they meet him later. It’s a stretch, but people can and do live to be over 100 - and I figured that Muntz, living in the wilds of South America all these years, was eating a healthier diet (natural/“organic,” more fruits/veg/fish, no “junk food”) than he would have been “stateside,” plus his obsession with finding The Bird was keeping him more mentally and physically active than he would have been if he’d ended up sitting in a cushy chair at the Old Explorer’s Home.[/spoil]
As far as the filmmakers go, I agree that [spoil]Muntz’s age probably originally had to do with the “finding the secret of eternal youth” plot that they dropped.[/spoil]
hmm…what an interesting explanation you have.
yeah, i heard that too. they made a right thing to not add the plot into the movie. lol
Edited. There is no need to quote the entire post. – Mitch
I think their ultimate plot/character choices for Muntz worked best because:
First -if he’d been searching for the secret of eternal youth, they would have had to give us a reason why - why is that so important to him? Whereas, by having his discovery rejected and his integrity challenged, we understand why he’s so determined to prove himself and clear his name. The frustration of “I really did see / do that, but no one believes me!” is a motive even young kids can understand, and actually makes him sympathetic to begin with - it’s only when he gets all paranoid and starts killing people that he becomes a “villain.” Second - I don’t think protecting Kevin’s Eggs would have been as compelling as protecting Kevin. The way Kevin is established as a character we love, with a distinct personality, makes us care and worry more when she is hurt and captured, upping the emotional stakes. The Egg would have just taken us one more (unnecessary) step removed from that.
One of the things that I think makes Up so good is that the story is so well “streamlined” - there’s not a lot of distraction or unnecessary complications, everything really holds together and pulls in the same direction.
Oh, and this is just my opinion, but I think Muntz would have to have been no younger than about 30 when we first see him - just because he’s been [spoil]adventuring long enough to have collected everything we see in his airship (which he also had to have time to design), plus whatever is housed at the various museums he mentions, and that all apparently happened before he took off for South America at the end of the newsreel.[/spoil]
Edited for spoiler content. – Mitch
Also keep in mind, [spoil]young Carl wasn’t a baby. He was at least 8 or 10 years old when they showed him as a child. So if Muntz really was 20 in the news reel and Carl was 10, then Muntz would have been 88 years old in the future.[/spoil]
Since Russell’s official age is 8, I always figured Young Carl was also supposed to be 8, drawing a sort of connection/comparison between them.
karly05: yeah i think the same thing too.
okay let’s do the math:
Carl’s age: 78.
Hence, he’s born in 1931.
Let Young Carl’s age be 8.
The movie he watched was in 1939,
Where Charles Muntz’s age approximately 30 (the ideal age).
Hence, Charles Muntz’s born year: 1939-30=1909.
Therefore, Charles Muntz’s real age: 2009-1909=100.
Taking the diet/the lifestyle of Charles Muntz in [spoil]South America/Venezuela[/spoil], he’s quite a tough-nut-to-crack old man. And humans do live until 100+ years old. And Charles Muntz was one in a million. Or he just take [spoil]Kevin’s egg[/spoil].
In conclusion, the answer is approximately 100.
AND I think this mystery solved? Or we have to refer Pete Docter for all this?[/u]
Edited for spoiler content. – Mitch
Wow, reading awfully far into this! I didn’t know about the whole fountain of youth thingy, good thing they threw it out, it would have made the circumstances too far out. I figured he’d be in his late 90s or so. He did seem a bit too active though.
It’s true. The writers agreed that the ‘Fountain Of Youth’ part shouln’t be in the movie or it will be absurdly absurd.
Actually according to the Art of Up, Carl was born in 1927, and the story takes place in 2005. And pushing it, Muntz could probably be 25 in the newsreel, so he can be around 95.
O-M-G! I really, REALLY have to buy that book. NOW! 
Yeah, I’d love a copy as well. I need to get some swag!
Maybe Pixar does love making audience wondering…hmm…
Whoa ffdude1906, you’ve leveled to Shark Bait in just one day!
Lol, yeah, i have
Anyway, back to the topic, I think Bryko nailed it on the head, since it gave Muntz’s actual BIRTH YEAR, that’s crazy. Pretty active for an old fart, but then again, Carl gets the same way, so,…
Btw, Bryko, we’re awfully close on Up counts,… -_- IT’S ON! 
i smell rivalry…