Testosterone ranges were created using population studies, using thousands of men. They just randomly tested men, whether they had any symptoms or not, and said "these are the average levels of testosterone in men". They did not make distinctions based on age and they did not exclude men with potential hypogonadal symptoms.

With that in mind, ranges are almost entirely useless in the diagnosis of hypogonadism.

The range is very very broad. Normal testosterone, based on most laboratory criteria is 250-1000. Some labs use 300-1200. Some say that the average is 350-900. The fact that there is no consensus on what is "normal", proves that there is actually no normal.

Also, a man may be blessed with a high normal testosterone (say his normal is 1000. But then he starts feeling bad, and he goes to the doctor and sees that his testosterone level is 550. The doctor will say "Your testosterone is completely fine". Well, actually, no it isnt. His level is half what it should be. This is known as relative hypogonadism.

So long story short, any good medical provider will treat hypogonadal symptoms regardless of level. If their symptoms resolve on TRT, then they had hypogonadism. If their symptoms dont resolve, then their symptoms are from something else and they can stop TRT and explore other options.