My fsh, lh, and free testosterone are all in normal range, but they are on the lower end of the scale. does this have / had it any impact on penis growth to reach genetic potential? would penis be different today if those hormones were higher?

There is no way to answer this question with certainty. There are a number of factors that influence penis size, including genetics, hormones, among others. FSH, LH, and testosterone vary throughout a man's life. There is no way to know what those hormone levels were years ago. Even if the levels were known, it's nearly impossible to accurately determine the degree of impact on penis size.