How old is Mr. Bounderby?

Mr. Bounderby's age is alluded to in Chapter 4 of the novel. Dickens writes that Mr. Bounderby "looked older; his seven or eight and forty might have had the seven or eight added to it again, without surprising anybody."
This is a rather roundabout way of saying that Mr. Bounderby is 47 or 48 years old, as indicated by, "his seven or eight and forty." Dickens also writes, however, that Mr. Bounderby looked perhaps 54 or 55 years old, as his appearance would have caused people guessing his age to add another "seven or eight" to his actual age.
Mr. Bounderby looks older than he is because he has no hair, and because he is a large, fat man ("inflated like a balloon") with a "puffed" head and veins that "swelled" in his temple. From this appearance, it is obvious that Mr. Bounderby doesn't live a particularly healthy life.
Mr. Bounderby might account for the fact that he looks older than he is, however, by referring to his difficult upbringing. He says, later in Chapter 4, "I was born with inflammation of the lungs, and of everything else . . . that was capable of inflammation." We learn later in the story, however, that these stories about his difficult, impoverished upbringing are all lies. He hasn't had to fight his way up from the bottom, with no help from anybody else. He has, in fact, lived a comfortable life and has benefited from lots of help along the way. His older appearance is simply a consequence and reflection of his gluttonous, unhealthy lifestyle.