The baseline
To get a motorcycle permit or endorsement in Washington you must be at least 16 and hold a valid Washington driver license. The endorsement is added to that license; it is not a standalone credential.
That ordering matters for families. A teenager cannot shortcut into motorcycling ahead of a car license. The driver license comes first, which for most 16-year-olds means drivers education and the graduated licensing process before motorcycling is even on the table.
Two extra requirements under 18
An approved safety course is mandatory. An adult may choose between testing at the DOL and taking a course. A minor may not. The course is required, and it cannot be substituted with self-testing.
A parent or guardian must sign consent in person. The consent form is signed at a licensing office, not printed and mailed. A parent also has to give permission for the minor to enrol in the safety course itself.
There is a practical consequence attached to this: a minor cannot complete the endorsement online through License eXpress the way an adult can. They must attend a licensing office with the parent or guardian.
Permit restrictions apply regardless of age
The instruction permit rules are the same for a 16-year-old as for a 40-year-old: valid 180 days, no passengers, no riding during the hours of darkness, and a maximum of two permits in any five-year period.
For a teenager whose riding time is after school in a Washington winter, the darkness restriction is the binding one. It is worth planning the training around daylight rather than assuming there will be time to practise.
What the DOL does not say
Worth being straight about a genuine gap. For car licences, Washington applies an intermediate licence with passenger and night restrictions to drivers aged 16 and 17. The DOL does not publish an equivalent set of post-endorsement riding restrictions for under-18 motorcyclists.
We are not going to invent one. If your family needs certainty on this, ask the DOL directly rather than relying on any website, including this one. What is documented is the permit-stage restrictions above and the mandatory course and consent.
The parent conversation
Most parents arrive at this having already lost the argument about whether. The useful question becomes how, and there the answer is unambiguous: trained, geared, and on an appropriate machine.
Washington's crash data is blunt. A large majority of riders killed in fatal crashes have no record of completing a training program. A course is the single highest-leverage thing available to a family in this position, and for a minor it is required anyway.
The machine matters nearly as much. A first motorcycle with more power than the rider can meter is the most common way a competent new rider gets hurt.