In terms of age, being older is always better for predicting loss. I would say that you are at a questionable age for it. 25yo men get HTs every day, but that does not prove it is a good idea.
(And talking to those men again when they’re 30yo does not prove much either. The hair loss problem isn’t going to stop worsening and you still have 60-70% of your life ahead of you.)
Much depends on the situation.
The people who defend young HTs often say things like “I’ve already lost most of my hair even though I’m young, so what’s the harm?” But that is flawed logic. If you’ve “already lost most of your hair,” how are you judging that? How is the end-point determined? There are NW#7s out there even if you haven’t seen one in your family yet. (And some of the NW#7s eventually get so bad that they probably should be called NW#8.)
Let’s say you are in your early 20s and you have already lost almost as much hair as your male relatives did at age 50-60. That does not automatically mean that most of your hair loss is over now. It may mean that you will continue to lose more hair for a long time, and eventually set a new family record for hair loss.
But even after saying all that, I also think there is a huge difference between age 20 and 30. LOTS of guys say that they lost A LOT of hair during this period in their lives. 20s are a decade that is very high in androgens, and I believe the late 20s are quite high in DHT in particular.
If you’re 25, you’ve already lost/losing a large amount of hair, and you’re serious about getting a HT? I vote to see if you can stand waiting until you’re 27-28 before you go under the knife. (It might take half a year just to schedule the procedure anyway.)