Generally to win in the Veteran group you have to post at least a -18 and it's usually a -19 or -20.
There was one time i had a -21 and there was only one player left with about 3-4 hours to play that had a shot at it.. he ended up tieing me and he won on whatever tiebreaker they use.
for the most part it requires some luck to get the right winds in order to make some par 4s driveable and the par 5s reachable in two. a random hole out helps out a ton as well.
in general hurricane winds on st andy and chambers and RSG will hurt you. however if can get lucky with the right tail winds on the right holes it can make the difference.
Top 20 is usually a -16 or better maybe as low as -15 will do it.
also it depends on the bracket that you're in. Some groups will win with a -18 and others it takes a -21.
i usually don't look at the score i need. I prefer to not know. -20 is doable but odds aren't great. pray for good winds.
I'll play tonight if i have time.