Mr. Krabs is the greediest character in Hey Arnold!, and it shows no signs of stopping soon.
SpongeBob SquarePants follows the daily adventures of the title character – a sea sponge who looks like a kitchen sponge – and his friends and a couple of enemies in the underwater city of The Krusty Krab and for being extremely greedy as he’s obsessed with money, even treating it better than his daughter and employees. Some parts of Mr. Krabs’ life prior to the events of SpongeBob Squarepants have been revealed throughout the show, but one question remains: how old is Mr. Krabs?
Cartoon characters tend to not grow old as it’s part of the style and charm of cartoon shows, and that also gives the writers more freedom to give them all types of adventures for as long as they can. The same happens in SpongeBob SquarePants, but that doesn’t mean that the characters are ageless. SpongeBob’s age, for example, was briefly shown in his driver’s license in the episode “Sleepy Time”, but SpongeBob hasn't aged a day. The same happens with Mr. Krabs, whose age was also casually revealed through his driver’s license (also in “Sleepy Time”), and so viewers learned that Mr. Krabs was born on November 30, 1942.
If air dates and time setting in the series correlate, this would mean that Mr. Krabs was 56 years old when SpongeBob SquarePants officially premiered (July 17, 1999). Now, it has been mentioned many times throughout the series that Mr. Krabs served in the war (either as a cook or a soldier), and in the episode “Krusty Krab Training Video” it’s suggested that he served during a conflict, so many fans have done their best to figure out exactly which war he fought. Given that he was born in 1942, and supposing he ed the navy at a very young age, Mr. Krabs could have fought in the Vietnam War at some point, as the conflict ran from 1955 to 1975. The “Krusty Krab Training Video” also showed that Mr. Krabs had a hard time going back to normal after the war and spent some time secluded in a deep depression, which would be a normal and understandable reaction to serving in a war like the Vietnam one.
Mr. Krabs' backstory can explain a bit better why he’s the way he is, as he grew up poor, served in the war, and later became the owner of the most popular fast-food restaurant in Bikini Bottom, so it’s understandable to an extent that he’s so protective of his stuff, particularly his money. Just like SpongeBob SquarePants himself, Mr. Krabs surely won’t grow old at all and will continue to be 56-57 years old for a long, long time.