I live in the Portland metro area but I am not aware of any sites that have age restrictions. (I would be interested in knowing which ones you have run across.) In our local trips (2-3 hour drives) we stay exclusively in Oregon State Park campgrounds, so maybe that is the difference.
There are a lot of private parks in and around Portland. A nice one about 30 miles north is Bayport RV Park in Warren, OR. It is situated right next to Scappoose Bay Marina. It is north of Portland on Hwy 30 and is less than an hour drive into the central city.
https://www.portofcolumbiacounty.org...ark-campground
The closes state park is probably Ainsworth State Park. It is about 35 east of Portland on Interstate 84. Also an easy drive into town, especially if you need the south or east sides.
P.S. - - Essvar is right, though. Portland proper has become a cesspool of bum camps and old, crappy rv's parked anywhere and everywhere. Don't know why the city puts up with it.
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