Q: Do journals allow an undergraduate as the first author?
Most journals do not have any specifications about the qualifications of the author. As long as the quality of research is good, most journals would have no problem if the author is an undergraduate. Having said that, conducting original research and writing a high-quality article is a daunting task and requires a great deal of knowledge and expertise in the field. Achieving this might be difficult for an undergraduate student.
However, there are certain journals that are dedicated exclusively to the publication of undergraduate research. It might be easier for an undergrad student to publish in such journals. The provides a list of popular undergraduate journals.