Actors who always seemed old no matter the role

Patrick Stewart. Even in his early roles, when he had hair, he looked at least middle aged.

Edit: I didn't notice that he'd already been mentioned.

One that some people might not agree on is Don Knotts.

Robert Duvall looked old even in his twenties.

Harry Dean Stanton.

https://www.country1071.com/wp-content/uploads/sites/40/2017/09/hds-1024x576.jpg

Burt Mustin always played an old man. He never seemed to change throughout the decades.
Gus, the fireman on Leave it to Beaver in the late 50s/early 60s.
In the 70s he appeared in so many shows looking the same. All in the Family and Barney Miller, to name just a couple.
You may read about him here.

https://en.wikipedia.org/wiki/Burt_Mustin

How about Harry Morgan? He was in High Noon in 1952 at age 37. At ages 52-55 he was Det Gannon on Dragnet, then Col Potter at age 60. At 28, he was Henry Fonda's sidekick in The Ox Bow Incident. I don't remember how he looked in that.

I'll add a couple more names with Edgar Buchanan and Will Geer. They'd be over 100 years old if they were still alive. Actually, over 110 years old.

Max von Sydow.

Leslie Nielsen

Charles Lane. Great character actor. Among many other roles, he played Mr. Potter's "little rent collector" in It's A Wonderful Life. He was active in roles for 75 years, and lived to age 102.