He started out as a sanitary inspector but ended up as a company president.
and, as such, contrasts semantically with 'end up'.
'Start off' means little more than 'start', but may often have the slight additional implication of the first step in a perhaps potentially lengthy or complex process, e.g.
Proving Fermat's last theorem is likely to take us years, but we could start off by doing a few preliminary equations.
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