"Finished school", in British English, means that he finished secondary school. After that, he completed a university degree (presumably a Bachelors) in business studies.
In this context, "when" means "after", and "did" means "completed".
2014년 5월 19일
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Without any further context, you would understand the phrase 'did a degree' to mean completed a course of study - probably a three/four year course at university - and graduated with a degree at the end of it.