That number wouldn't be particularly meaningful without also knowing the number of 30+ players in the slam draws since 1970, and it's far too much work to look all that up and tally everything just for a thread like this. I think the bottom line (wins) is significant all by itself.
Ya I understand what you mean. It's still important to note what you're actually estimating.
The two events here are:
A = 30+ year old wins the world tour final
B = 30+ year old makes it to the world tour final
What you're estimating is P(A and B) not P(A|B). Since P(A and B) = P(B) * P(A|B), they won't be that close if P(B) isn't close to 1.
The equivalent for slams would be:
C = 30+ year old wins a slam
D = 30+ year old makes it into a slam
So you are estimating P(C and D). But, P(C and D) = P(D) * P(C|D) and I think since you only have to be top 100 to make it into a slam, P(D) would be pretty close to 1. So your estimate for P(C and D) would be pretty close to P(C|D), which is what you want.
Basically, your results rely far too heavily on the fact that it's much harder for a 30+ year old to even make the WTF than it is for him to make it into a slam. Something which no one will dispute.
A much more meaningful and interesting question is how does a 30+ year old who is good enough to be top 8 do against the field in the WTF.
Just going back to 1995, all of these did not have a 30+ year old in them:
1995
1996
1998
1999
2006
2007
2008
2009
2010
and 1997 is not in there only because 30 year old Muster was an alternate who only played 1 match.