The wiki says it starts spawning around level 16 and can be found at ranger station delta but I can't find it there or anywhere?

They spawn closer to the front lines, alpha and bravo, I think.

Can't find them there either? Am I bugged out?

They also seem to hang out in Camp Forlorn Hope a lot. If you hang out in one of the larger Camps (Golf, McCarren) you can sometimes hear random people comment on "special rangers" being moved to the front. That's when you can start finding them.

Do not treat the wiki as gospel. A lot of it is educated guesswork.

You may be required to progress further in the main quest chains.

Do I have to go to the fort and retrieve the platinum chip first?

No in hidden valley the BoS elder tells you that a ranger is camping nearby and you can kill him and get it

I Think he means the veteran ranger armour.

I started seeing them everywhere at NCR locations after I did the first mission from the NCR ambassador on the Strip.