It is possible for a man to be 73 years old and still be fertile.
The fertility of a man depends mainly on the survival rate of his sperms. For some men, even at the age of 70 or above, the sperm survival rate can still be high, and therefore fertility is possible, although the quality of the sperms may decline as they are no longer in the optimal age for reproduction. However, there is also individual variability in specific fertility.
For 73-year-old men who want to have children, they must first undergo a routine semen examination to judge according to the number, density and vitality of sperms, etc. At the same time, it is also necessary to regulate the underlying diseases, especially prostate diseases, etc., before having children so as not to affect the quality of sperms.