Hi Joel, I also used the 20-25% split. Its a number I've had in my head from doing my Business Plan 10 years ago. There's lots of ways you can measure it I guess (people who played once/year, people who play 10 rounds+, club members, social golfers, differs by country etc etc). However, in general I think most in the industry here are comfortable with something like an 80:20 split. I did not have much time to search but here is some basic info off the Golf Australia website. It's a little dated. It's Australia only. But its probably indicative of a mature, western golf market?
Male 2008 942,900
Female 2008 238,200
Total 2008 1,181,100
How often do they play?
20% play less than 6 times per year, whilst 27% play more than once a week.
What % of these are female?
20%. The female % of the population is 50%!
What % of the population plays golf?
Approximately 6% of the population.