The copula "là" is not needed when linking a subject to a predicate adjective and sentences which resemble to "tôi là già" or "anh ấy là cao" wouldn't make sense.
It's also not okay at all if you omit "là" when linking two nouns. We always need it in these cases.
Hello jdberry300. Remember that "g" and "gi" are two different letters and represent two different sounds. "Gi" (as in the word "giàu" above) represents the sound /z/ like z in 'zoo' while the letter "g" shows the sound nearly like g in 'get'.