Apropos of SF Barnes' longevity (though I realise you're talking Tests), a couple of startling facts:
In 1928, aged 55, he played for Wales in two first class matches. In the first match, against the West Indian touring team, he took 7-51 and 5-67 and took Wales to an 8 wicket win. The West Indians said he was the best bowler they faced on that tour. The next month against Lancashire he took 6-58 and 2-29.
In 1929, now aged 56, he played in two more first class matches, against the touring South Africans. In the first innings of the first match he took 8-41 off 32 overs against a strong batting line up (only 9 wickets fell as one man was taken ill). Rain washed out the second innings, with Barnes taking the only wicket to fall. In the second match Barnes took the 6 of the last 8 wickets for 23 in the first innings and bowled a spell of 4-10 in the second.
Barnes was still averaging less than 10 runs per wicket in Minor Counties cricket when past 60, and was still good enough to earn a living in league cricket when not far short of 70.
(with thanks to Ralph Barker, "Ten Great Bowlers")