If one thing is for certain, it is that the speaker of this poem loves the word "If." He loves it so much he uses it 13 times. In a poem that's only 32 lines, that's nearly every two lines. Now the speaker doesn't use this word a million times because he has some kind of problem or anything like that—far from it. By the end of the poem, we learn that the speaker is talking to his son and the poem is partly instructional. The speaker, then, is not just a father, but a father who is putting his parent-as-teacher cap on for all to see.
Lots of parents, when they're in teacher mode, have this way of appearing very wise, and the speaker of "If" is no exception. The very fact that he is able to list off all the different things his son must do if he wants to become a man tells us that he has been around the block a few times and is familiar with just about every roadblock his young child will have to negotiate in his journey through life.
Now, even though the speaker definitely resembles your incredibly smart father, or your very wise grandpa, he also comes across like a sage counselor of sorts, the quiet guy in the corner that is usually reserved, but every once in a while decides to speak just to show that he knows more than all the blabbermouths in the room. Just think of a guy like Maester Aemon from Game of Thrones and you'll have an idea of what we mean.
Again, we get this vibe from the speaker because, well, he gives such detailed explanations about every possible little situation. We can't help feeling that the speaker doesn't just know about stuff, but has seen so much of it that he knows exactly how things will play out: truths will be twisted by knaves to make traps for fools, men will lie like crazy to get ahead, the things one has spent one's whole life building will collapse… you get the idea. In short, this guy has seen it all, and lived to tell the tale.