Since the end of WWII, 72 pace bowlers have taken a minimum of 10 wickets after turning 33. Since the turn of this century, that number drops to 22.
Looking at the data since WWII, of the 72 pace bowlers, 27 had a strike-rate under 60 (but only 9 of those had a strike-rate under 50) and another 13 had a strike-rate under 70. The average strike-rate for these bowlers was 72.40.
After turning 33, Botham had a strike-rate of 101.4, Wasim Akram 78.6, Dennis Lillee 73.6 and Zaheer Khan 77.5.
On the other end of the spectrum, Joel Garner picked up 34 wickets with a strike-rate of 35.8. Hadlee proved ageless, with his strike-rate of 46.9, Marshall (48.0), Willis (48.5), Pollock (51.5), Donald (53.6), McGrath (54.4), Imran Khan (54.7), (Ambrose 56.0) and Walsh (59.3) all picked up a wicket under once every 10 overs after turning 33.
However, of these 72 bowlers, only 28 took 40 or more wickets after turning 33, and only 18 instances have occurred after 1980.
Regarding Test matches played - since WWII, 17 pace bowlers have appeared in 20 or more Tests after their 33rd birthday and another 18 appeared in 10-19 Tests. So less than 50 per cent of pace bowlers after turning 33 appear in more than 10 Test matches. The average pace bowler has bowled in just 23.59 innings after their 33rd birthday.
If you narrow the criteria to 20 wickets taken after 33, there have been just 6 pace bowlers to have taken more than 20 wickets at a strike-rate under 50 (Garner, Cowie, Hadlee, Marshall, Willis and Bedser) and just 21 with a strike-rate under 60. Very few bowlers manage to survive after their 33rd birthday, and those that do, see a noticeable drop off with the exception of a few aberrations. I will get the full article up tomorrow.