[ט' אדר תשי"ג]
...כן אתענין לדעת מהנעשה ע"ד שידוך המתאים בשביל בנו שי'. ועתה אשר ראה כבודו בעיני בשר, יכולת השי"ת בענין זיווגים, אף שנראה לו שזהו דבר קשה, וגם רז"ל אמרו שקשה כקריעת ים סוף, בטח הרי יוקל הענין גם אצל בנו שי'. ובלבד שישתדל כדרשת חז"ל, דרכו של איש וכו'. וידוע ג"כ העצה הוגנת של חז"ל שאין צריך להיות - בגיל - חילוק גדול ביניהם.
On the 9th of Adar, 5713.
...I am interested to know what is happening regarding a suitable shidduch for your son, may he live. Now that you have seen with your own eyes the ability of the Almighty in matters of matches, even though it seems to you that this is a difficult thing—and our Sages also said it is as difficult as the splitting of the Sea of Reeds—certainly, this matter will also be eased for your son, may he live. Provided that you make an effort as our Sages expounded: 'the way of a man...' And it is also well known, the proper advice of our Sages that there does not need to be—regarding age—a large difference between them.
Summary
The Rebbe encourages trust in G‑d's ability to arrange shidduchim and highlights the importance of personal effort. He notes that a significant age gap between prospective partners is not necessary according to our Sages.