Please accept my apologies for the delay in addressing your question. As I mentioned before, I was away for a time on vacation, and upon my return there were other matters claiming my attention until now.
I agree that it seems highly unlikely that Johannes, as a 94-year-old man, would have or could have fathered Valentin, even if he had lived that long. I doubt, however, that if he had done so, that it would have been a unique event in medical history. Stranger things have happened. More to the point, the Familienregister record upon which my data entry was based is, I must admit, ambiguous:
A note in the Family Register for the Winterbach Evangelical church, volume for affiliated churches (Rohrbronn, here), p. 123: "Johannes kam mit seinem Vater nach Ruъland. Dessen Sohn Theodor Hottmann ist am 2 Dez. 1871 in Ruъland geboren. Dessen Sohn Valentin Kurt ist in Berlin am 4. Oct. 1909 geboren, u. (word illegible) am 5 Febr. 1921 einen Fam. Reg. Auszug S. 123." [Johannes came with his father to Russia. His son Theodor Hottmann was born on 2 December 1871 in Russia. His son Valentin Kurt was born in Berlin on 4 October 1909, and on 5 February 1921 (requested?) an extract of the Family Register page 123.]
The usage "His son Theodor...." and "His son Valentin..." is the source of the problem, obviously. Admittedly, these sentences could just as well mean, "His (Johannes') son Theodor..." and "His (Theodor's) son Valentin...." If you wish to interpret it this way, I certainly could not object. Perhaps one day you or someone else will locate a death record for Johannes or some other document that will resolve the ambiguity.