Not necessarily, I got LORs quite easily from 2 professors 5 years after graduating. I was an above average student with both of them. They get those requests all the time. Generally an academic LOR holds more weight for graduate school admissions, and some schools require academic LORs. It varies from school-to-school. Often, when you fill out an application, it comes with a template you can fax/email a professor directly.
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