Both have a problem. Change the word "comparing" for "considering", then both are fine, and I would favour the first one.

The second one sounds more natural. However, I would replace the word “comparing” with the word “considering”

The second sentence is both grammatically correct and more natural: 2) "I’m far more reserved and introverted than he is, especially when comparing our ages."

Neither is natural, but the problem is meaning, not grammar. In #1, you use the word "compare" but you aren't comparing anything. #2 doesn't make sense because comparing your ages has no effect on how reserved or introverted he is. I'm not sure what either sentence is trying to say. If you explain some more, I'll make some suggestions. I really don't understand why age has anything to do with being reserved or introverted.