Whoever that someone is? Ignore them. They have no idea what they're talking about. Yoga is good for everyone medically cleared to do it by their doctors! It is important to have correct form, but anyone capable of doing the poses can benefit from doing them. I started yoga at 200 lbs, and I have never regretted it once. Some poses can be tough if you've got a big belly, or other parts are a bit bigger than they could be, but you can ALWAYS modify the ones you can't do!
Not only can they, but they SHOULD! an overweight person stands to gain the most benefit from yoga practice!
So if you wanna, go for it, and don't take fitness advice from whoever that was. They're making stuff up. :) www.ideafit.com/fitness-library/yoga-for-o