If I correctly understand the question, your friend did not assume the identity of another person for the purpose of obtaining that person's credit. That would have been identity fraud. What he did was use an alternate name. There is nothing necessarily illegal about that. The test is whether he used the alias fraudulently. If, for example, he made up a name to obtain credit because he suspected he would not have been able to obtain credit in his real name, he may be in trouble.
But if he did this 30 years ago, probably any applicable statute of limitations has long since expired.
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