As Seen on TV: When Mr.Krabs is filling out the paper in his office, he says "if I fire him, and make his successor do twice the work-". He then hides the paper, only to reveal it without hesitation after sponge-bob walks in. This means Krabs was thinking about firing Squidward.
Mr. Krabs' first dime is shown to be a stone wheel, suggesting that he has been around since prehistoric times. However, his identity card in 'Sleepy Time' reveals that he was born in 1942 and 'Hooky' suggests the Krusty Krab has been around since at least 1959.