physiologically, as long as a male is able to ejaculate, the sperm contained within the ejaculate is viable - i.e. alive and kicking. The male reproductive system is intentionally designed to produce WAY more living sperm than needed, as an 'insurance policy' if you will that if he ejaculates into a fertile female, pregnancy will result. Remember that typical sperm count for most adult males - even mature ones - is anywhere from 120-320 MILLION living, viable sperm cells - and it only takes one.
Unless he's had a vasectomy, his testicles have been irradiated (accidentally or intentionally) with sufficient dosage that produced sperm are either dead or incapable of fertilizing an egg, or his testicles have been removed, or other actual measures have been taken to prevent sperm from being produced, males are fertile until they die.
There are way too many guys, some well into their 70's, out there that believed the myth that after a certain age they can't father a child - and found out the hard way that's simply not true.
Also the old wives tale of taking hot baths or otherwise keeping ones testicles warmer than usual will render a man sterile is similarly a lot of bunk - and just results in unwanted pregnancy. While keeping ones testicles warmer than their optimal temperature does decrease viable sperm production, it in no way stops it or renders the sperm produced to be impotent - and besides - sperm is stored after production in the seminal vesicles inside the body, on either side of the prostate - even if it did have significant effect, taking a hot bath then having sex doesn't do anything for all the stored sperm a man has saved up inside him.
Your buddy needs to either get his gal onto birth control, or use condoms - but it sounds like their situation is such that they have other issues to worry about anyhow and right now would be a bad time for them to be bringing a child into the world in the first place.
