What daily commercial flight is the oldest / has been running the longest? Out of curiosity, what flight, currently still operating, has the earliest inception?

There are several ways to define this, and I expect available information will determine what definition is most useful. As an example, if a flight's inception date is the earliest date such that there has been a commercial flight on every day (or every week) between that date and today, what flight has the earliest inception date?

Also interested in a flight using the same aerodromes, or with the same airline, or even aircraft type.
According to the Georgia Encyclopedia one of the oldest flights operated by Delta was Love Field, Dallas to Birmingham, Alabama from 1929 up to 2000. Birmingham ist still served by Delta, but not from Love Field.

According to this the first flight from London to Schiphol was in May 1920. This route ist still in operation by KLM. But London at the time meant Croydon Airport.

On 27 May 1936 Aer Lingus made its first flight from Dublin to Bristol, while the route is also still in operation, the airfields changed. (wikipedia)

Take your pick.