Is it even possible? How can you look at a pic and say "oooo lovely pre-64' or Mod70...?
I tried above to explain the difference.
But, when the question is "how", the answer is knowledge and experience!
Many people on this forum are firearms enthusiasts, aficionados, experts, and they are studying and using firearms their entire life. (and many of them are in retirement years, or close to it)
So, dont think that this knowledge came overnight by accident.
If you will take my advice:
Start buying books on firearms. (and less internet)
All modern sporting firearms came from military design.
So, my advice to you is buy the book(s) on military rifles historical development.
And then, expand the library to modern hunting and sporting rifles.
When I was a kid, there was not many books around on firearms.
But, when I was about 9 years old, I managed to get the book "World war II - Small arms" by John Weeks, which I have read innumerable times. to the point of collapsed hard cover.
I vividly remember that book, and can still quote few sentences from it, after 40 years.
My grandpa had some hunting rifles, and one ww2 trophy pistol. One Rifle was mauser sporter clone, and about the pistol and that rifle I have read everything in that book.
Then, when I managed to get to those guns when grandpa was willing to show me, I tried to understand what the book was describing in and functions of that gun.
This is how, I started my firearm education. 40 years later, I am still studying the books read about historical guns, and modern ones, and use guns in hunting, and target shooting. Membership in three shooting clubs helps, because I can see or on occasion try various models
(I am not saying I am the expert, but I can at least follow what they are saying when the experts are talking)
So, start reading materials written by authorities on the subject. History and development and modern use. Read about the guns accessible at your place, and try to find their flaws, how they funckiton, and good things. Amazon and other sources are rich with good titles.