Is Anand the oldest player in the top 10 ever?

Or has there been anyone else that still remained at top 10 even when they're already around 50 years old?

I think Korchnoi was in his upper 50s before he was out of the top 10

Karpov was still top 10 in his 40s , don't know about his 50s . Lasker was  still top 10 in his 60s . 

As far as FIDE lists go, Korchnoi must be the answer. He was last ranked in the top 10 as late as January 1990, when he was almost 59 years old. It's worth noting that even though his ranking was rather unstable later on, he managed to be ranked No. 17 on the July 1999 FIDE rating list, at 68 years of age.

As for historical rankings, we can consult chessmetrics.com. Here are some data about two players who showed great longevity:

Format: player, last list where they made the top 10, age at the time

Lasker, April 1938, 69 years

Steinitz, August 1900, 64 years

Here... someone did an amazing video to show you! https://www.youtube.com/watch?v=2yxnOqOJbac 

Smyslov born 1921
played the Candidates' final against Kasparov in 1984 i.e. aged 63.

Smyslov seems to be the answer.

Smylov 9th at age 63

Korchnoi 10th at age 59 (still 17th at age 68 though)

Polugaevsky shared 10th at age 57

Tal 6th at age 51

Portisch 7th at age 51

In July 1970, Botvinnik was number 7 in the world, aged 59.

Why would it show that?

In darts, Phil Taylor was number 6 when h retired, aged 58 (in 2018).

#9
Lasker got 3rd at Moscow 1935 at age 66, which got him back into top 10.

Chessmetrics doesn't count.

I don't know

Korchnoi also won a National championship when he was 78 and 80

from wiki

"Korchnoi became the oldest player ever to win a national championship, when he won the 2009 Swiss championship at age 78.[58] He won the national title again a few months after his 80th birthday in July 2011 after a playoff game with Joseph Gallagher.[59]"

Oldest player in top 100:

"On the January 2007 FIDE rating list[56] Korchnoi was ranked number 85 in the world at age 75, the oldest player ever to be ranked in the FIDE top 100. The second-oldest player on the January 2007 list was Alexander Beliavsky, age 53, who was 22 years younger than Korchnoi. As of 2011, Korchnoi was still active in the chess world with a notable win (in Gibraltar) with black against the 18-year-old Fabiano Caruana, who was rated above 2700 and 61 years Korchnoi's junior

Good to know.  If everyone who didn't know posted this, it would just be spam.

this just shows that age doesn't matter and anand is still kicking butt even today!

Several equestrian olympians (jumping and dressage) over the years have been in their 60s and 70s, even within the last couple of years.

Dead people rarely make the top ten list.

They tend to lose too many games on time.