Just read the story. Alfred's father served Thomas Wayne as butler, and Alfred did not want to go into domestic service, but his father made him promise to do so on his deathbed. He does indeed show up a few years into the Batman/Robin crimefighting partnership.
Alfred slims down in one story by going off to fitness camp, feeling he needs to be in better shape to help two crime fighters. He's the original portly design at the beginning, and when he returns he's more like the Alfred we're all familiar with.
In my head canon, Alfred Beagle (his stage name) had just finished playing Falstaff in rep (HENRY IV and THE MERRY WIVES OF WINDSOR). A committed actor, he actually put on extra weight to play the part. So he was stil portly when he came to work for Mawster Wayne. And it was taking him some effort to lose the pounds, so he went to the fitness camp to trim down.
Alfred Beagle was not only portlier than the later, more familiar Alfred Pennyworth, but also, I believe, somewhat shorter. That must have been some fitness program that not only reduced weight, but also increased height.
Buried Alien (The Fastest Post Alive!)
Buried Alien - THE FASTEST POST ALIVE!
First CBR Appearance (Historical): November, 1996
First CBR Appearance (Modern): April, 2014