My cat is almost 5 years old. She is the type to overeat to obesity, probably because she was abandoned at ~1yr by her previous owner. For half her life my partner and I have been feeding her like clockwork 3 times a day, minus all of 2-3 weeks of vacations where our roommate took over.
I have to exert a constant effort to maintain our bedroom door and the rubber that I lined on the jamb to prevent her from rattling the door at 5am to ask for food - the paint is a lost cause. We have a white noise machine. We ignore her cries for food. We ignore her pawing things off our desks. We have a system to keep track of food we give her so she can't "trick" the other person. She knows exactly when we feed her (the meows get cranked up a notch about an hour before food time) but despite not giving in, she keeps acting like meowing at us is going to go anywhere.
No luck. And we know we're not underfeeding her - she's getting the calories appropriate for her (currently normal) weight, is being fed wet food, has fresh water, lots of attention and toys, all that stuff.
Unfortunately we have to give this up because we've got a baby on the way, and it's just so frustrating to lose 2+ years of effort put into having her not weigh 18lbs...