This will be sort of the quick and dirty big dumb calf - if I don't answer your question let me know
You say he is nursing - how do you know? (not trying to be a wise a** but a lot of the big dumb ones suck on the udder not teat or suck on their tongue and don't really nurse). I can think of a couple reasons why a big -dumb (BD) calf would not be bouncing at 7 days of age
1) he is big and dumb but at 7 days I would rule out a couple of things
2) is he really nursing? can you weigh him? at this age he should be getting a minimum of 2 quarts 2x per day - if he was weighed (vs taped vs the eyeball weight) I would expect him to weigh at least 120 and probably more like 125 if he was getting adequate nutrition. After he nurses does his belly feel full. A little nutridrench per label is probably not a bad idea. If you offerred him a bottle would he take it?
3) BD calves are less likely to absorb colostrum, heifer colostrum is less "potent" than cow colostrum - so he is a set up for infection. Does he have a fever? Does he have a naval swelling? Joint swelling? Nasal discharge etc?? Any chance he has an infection?
4) I assume he is getting up and down by himself and moving around - if he is nursing and getting adequate nutrition and not infected then he is likely BD- and tincture of time the lightbulb will go off....good luck DL