Any women over 50 with success stories / suggestions?

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I need to lose about 40 lbs and it's getting harder to lose weight as I approach 50. I've been cutting calories to 1200-1500 per day. Basically I'm eating fruit smoothies for breakfast and lunch (frozen fruit, flax seed, unsweetened almond milk, and greek yogurt), and then a small dinner of usually chicken and vegetables. I had done this for about 3 weeks before we went on vacation and lost about 8 pounds. Went to Disney and gained 4 back! We walked sooooo much but I also didn't really watch what I ate so I guess that's not too bad.

But now that I'm home I really need to do some serious weight loss. I would really love to be able to drop 10-15 pounds in the next 3 months. Is that even possible at my age? If so, how can I do it?