First we look at the longest-lived Test cricketers:
From Wikipedia:
Only one Test cricketer crossed a century here, South Africa’s Norman Gordon (1911-2014). He played in 5 Tests against England in 1938-39. He is also 4th on the list of the longest-lived first-class cricketers.
Then there is this list from Cricinfo’s records section (not Statsguru):
https://stats.espncricinfo.com/ci/content/records/283740.html
Screenshot of this on 24 Mar 2020:
If you consider “famous” players who played in 25 or more Tests, the oldest would be Wilfred Rhodes (95/252) followed by Syd Barnes (94/251) and Bob Wyatt (93/353).
The oldest Test player from India is MJ Gopalan (94/198) followed by (the strange case of) C Ramaswami (93?) and MK Mantri.
Next we look at the oldest living Test cricketers today:
From Wikipedia:
https://en.wikipedia.org/wiki/Lists_of_oldest_cricketers#Oldest_living_Test_cricketers
As on 24 March 2020:
Again, this includes some lesser-known players. For a better idea we go to Cricinfo again:
https://stats.espncricinfo.com/ci/content/records/283742.html
Screenshot of this on 24 Mar 2020:
Taking a minimum of 25 Tests, the oldest well-known player is the last of the 3 Ws (Everton Weekes) at 95+ followed by John Reid at 91+, Neil Harvey at 91+ and Colin Macdonald also 91+ . The last two played in Laker’s Test in 1956.
The oldest from India are Datta Gaekwad (91+), CD Gopinath (90+) and CT Patankar (89+).