The name is correct
矢谷貞夫君 Yatani Sadao-kun (going down vertically, right side). Kun is honorific suffix usually applied to young men.
The big letters going down vertically (also right side) are
祈武運長久 (pray for long-lasting good luck)
which is nearly universal on all these flags, both fake and legitimate.
I can't read the name of the organization that presented the flag to young Mr. Yatani. The rest of the writings are just names.
I can't make out the seals. They are from the sending organization. Maybe a printing/publishing firm 眞囗出版社印 in the seal on the left. (I could be wrong)