There really is no predetermined age at which the light bulb goes off in their collective minds and they start consulting you for fashion advice
There are a lot of straight guys that are "confirmed bachelors" well into their 40s and nobody ever considers them gay, they just are not relationship oriented. I do not mean it offensively to hairdressers, but if you are not a hairdresser, you can keep it up just as long as the confirmed bachelors.
Also it is less the extended family's business than your immediate family since (if you are like my family) you exchange one note each year boiled down to "Doing well, how are you?" and maybe see them every four years or so (long distance.)
What is your relationship with them like? How often do you all see each other and how well do you all communicate - simple formal pleasantries or do they take an active interest in your life? Some "very conservative" people take coming out, especially at your age, to be a mark of maturity and independence and not a fatal flaw. But it is always easier to tell the extended family if you have a partner there and they can see someone is looking after you