The Gemara tells us that the Sages encourage a couple not to marry, for reasons of compatibility, due to age differences. However, a major theme of the mesechta is the Yibum is the ideal in form of the mitzvah. Itbseems that the issue of potential katata, outweighs the current obligation to do yibum. Don't we usually focus on the current chiyuv despite the potential problems down the line.
Aaron B, Neve Daniel, Israel
Thank you for your question! I think the answer is that even though we know that the Mitzvah of Yibum is Kodem l''Mitzvas Chalitzah, the Gemara uses Drash and derives from the verse, "v'Dibru Eilav," that the Dayanim should speak to the man, eye to eye, and give him advice. When this Halachah is derived from a verse in the Parshah of Yibum, we assume that this is part of the way to fulfill the Mitzvah. We find the same idea on Daf 4a, that we do not force a woman to marry a Yavam who has Shechin, and it is learned from verses as well.
On a personal note let me add that it does not surprise me that Chazal understood that there is no point in a Mitzvah that brings people into a terrible relationship.
Best Regards,
Aharon Steiner