This is the one I came to post.
Agree.
If this isn’t impressive enough, consider a ~36 year-old Woody Allen playing sperm in Everything You Always Wanted to Know About Sex * But Were Afraid to Ask (1972).
In the movie Grease (1978):
Stockard Channing (Rizzo) was 33 years old
Olivia Newton John was 28
And they played the roles of high school seniors.
The example that comes to my mind is Joan Allen in The Mists of Avalon TV miniseries. She played Morgause at the age of 13 in the beginning, when when she was 39. Of course, the character aged to maturity over the course of the miniseries.
Leslie Howard was 43 when he played Romeo in 1936.
D’Arcy Beth Carden (age 39) on The Good Place plays Janet (age infinity).
What do I win?
You win a re-read of the OP.
Just what I came in to post! Probably the most realistic old-age makeup I’ve ever seen (scroll down a little here), and Hoffman’s acting was more than up to the challenge: http://thegreatwesternmovies.com/2014/03/03/little-big-man/
Another good one. And consider James Daly, 51 at the time, who played the 6,000-year-old Flint: Flint | Memory Alpha | Fandom
And, according to an NPR interview she gave at the time, had to drink a lot of very thick milkshakes in order to plump up like Mary Todd Lincoln.