I think it's pretty sad.
Statistically it's more likely that he'll die before age 90 than survive that long. Although it's not impossible, as just over a third of American men aged 83 will live approx. 6 more years at that age (according to US stats).
However the chances of him still being alive in 2041 when the child is about to reach 18y/o, are tiny. Less than 1% of men his age now, will live past 100.
There is also a higher likelihood of genetic issues, which is a much bigger risk factor given his age. Sperm may be replenished at regular intervals but the quality of the sperm produced deteriorates as part of ageing.
I hope for both their sakes that everything turns out well, and that he enjoys good health for many years to come. However my overall view is that this is a classic case of "just because you can, doesn't mean you should".