Dear @many723,
That’s a great question and I think the real answer is we don’t know. There is some evidence that maybe it is different: there are particular genotypes in areas of the world where adult or horizontal transmission is the more common route (e.g., Genotype A in North America and Western Europe). This appears to be more responsive to interferon and results in more HBsAg-loss if there is cessation of long-term nuc therapy. Whether this is due to the genotype itself or the mode of acquisition is not very clear.
As mentioned by other users, anti-HBc IgM is seen when a person has been exposed to the virus for the first time in the last few months. The result of this exposure (whether it becomes chronic, or if it is cleared and is an acute infection) depends on multiple factors, including age as you’ve just mentioned.
We have a few threads about this: Lifestyle changes, nutrition, and supplements for hep b, Food, Activity, and habits alternatives guid; and Vices - alcohol marijuana etc.
Hope these help,
Thomas