First, I don't think the "Bike Mechanics" forum is the best place to ask this question. The "General Cycling" or "Advocacy and Safety" forums may be more suitable. But, now that you asked.....
The Tour de France and all of the other Pro Tour races are team events and the teams are granted entry by invitation, not as individuals like most running races. I don't believe there is any contractural prohibition for women to participate in the Tour de France, or other Pro Tour events but first one would have to make one of the team rosters and, frankly, the performance capability between the best women and the best men is still insurmountable. For example no woman has come close to winning Boston, New York, London, or any other major marathon and the woman's world's best time is still many minutes behind the men's best. Competing as individuals that is no problem but for a team event it is.
There are many races specifically for women and, indeed, there is a Woman's Pro Tour equivalent but they are not run simultaneously with the men's races on the same course. These women's races used to be far shorter and less demanding than the men's under the assumption that women were "too weak and fragile" to do more but that idea has generally been discredited, even in Europe, and women's races have become longer and harder recently. There may never be physical equality but there is a move to sporting equality.