Wow. That's a bizarre topic! I would suggest going to your local golf course and seeing if they have statistics on their membership. I am not sure where the PGA gets its statistics, but you might find some local evidence from your own golfing establishments.
Most credibly, as krishna suggests in post 6, you would want to do a survey, following some established protocol so objectivity is assured. The scientific method would be of help, as well as information about establishing a "representative sample."
You could support your individual research in two ways, look at the preponderance of professional golf tours for men versus that of women. Secondly, consider the number of men's leagues at public and private courses.
I agree with the previous post that a google or web search would be a good way to go on this. I would also suggest examining the winners and participants of the sport on high school, college, and amateur, and professional levels. Armed with these statistics, I would be surprised if you came up with anything other than the high level of presence of males ont he golf course. I think that you can use the evidence of how the LPGA (Women's Golfing Association) is facing intense crisis and difficulty, while the PGA (Male counterpart) finds itself enjoying relative tranquility and calm. It is interesting to note that when economic troubles besiege the nation, the women's golfing association has to modify and endure difficulty, but not the men's. This might be another evidence to substantiate the idea that men are mostly on the golf course.
The other answers give you excellent suggestions. Here is a piece of information that you could begin your argument with if you so desire. Many people mistakenly assume that the word "golf" derived from the acronym "Gentlemen Only, Ladies Forbidden." While this is simply a rumor about the game, it would be interesting to discuss why the game itself is so connected to gender issues that many people find the rumor plausible.
It will be hard to prove, but you can begin to do some detective word in a few ways. You can see how big the men's PGA is and compare that with women's PGA. You could also look at high schools and see how many schools have boys teams and girls teams. You could also get an impression by going to a driving range and making estimations of men and women. This will be more impressionistic, but it can help in making general statements. You can also go to golf stores and seeing how big the men's section is compared to the women's section. This might be the best way, since retailers do their research! Finally, you can ask golfers and get their opinions. There will be other ways, as you think about it more, but these suggetions should get you started.
I think probably the best way to find evidence for this statement would be to use an internet search engine such as Google. You could use the search terms "golfer demographics" or "demographics of golfers" or "golf demographics." Or you could try "percent of golfers men." Any sort of search like that ought to get you something.
I used some of these search terms and was able to find evidence like the link that I have included here. It says that 95% of golfers are men. Just based on what I have seen while playing, that sounds pretty plausible.
According to the USA PGA Tour , "78% of golfers are male." Knowing that, you could easily make an interesting paragraph on why that is, or if you have certain paragraph requirements, as to narration, description, cause-effect, etc.
The best and most reliable way of establishing the percentage of males versus females generally playing golf would be to do a sample survey of people actually playing golf on the golf courses. Perhaps examining record of the golf clubs for the people who have played golf there within a specified period may also be equally reliable. A third quite reliable method would be to to a survey of golf club membership.
All the above methods are likely to be quite costly and time consuming. It might be easier to study some indirect indicators such as composition of participants in golf tournaments and of spectators come to watch such tournaments.
Then we can also try to locate some secondary sources of information that may be available from periodical specifically devoted to golf. Search on the Internet may also provide some actual statistic, or at least indicate sources from which such information may be available.