As long as they are under a year old and have been castrated, the age won't affect the flavor. What happens, though, as they get larger they just tend to put on a lot more fat cover over the carcass. Also, the bacon just gets thicker and thicker. You can literally have slices of bacon like 4" wide from an older pig. I think it's awesome!
And do get the lard!!
And do get the lard!!