I don't think Tiiu is too old in the fashion industry's eyes. In fact, she's probably the perfect age now considering how young she started. However, I do think she's losing relevancy, now that new younger models like Ali Stephens, Toni Garnn, Ali Michael, Siri, etc. have become todays flavor of the month. Think of all the girls from Tiiu's modeling generation-- Hana, Marija, Caroline Winberg, Elise Crombez etc. They're all slowly disappearing from the limelight. The only girls from that generation that have maintained some sort of longevity are Daria, Julia Stegner, Gemma, Stam, Lily Donaldson, Raquel.
Bottom line is that Tiiu is still young enough to resuscitate her career. She has many more years of modelling left in front of her. BUT she has to make sure she joins the right agency (and maybe she should refresh her look), so that she gets more quality work for the rest of those years. The same way Cameron left Ford for DNA, Tiiu needs to do the same. If she does, I'm sure we'll see more of her.