合并成一句话The model is only seventeen years old.I thought she was older.

sorry,审题错误,改正如下：
I thought the model was more than seventeen years old.
注意用 more than,不是older than对不对呢？说话啊对或不对，这就要楼主自己判断了。卖瓜的王婆赞瓜 甜，我不会说自己错，你说是这理吧？ 或者还有种改法：She is younger than I thought she was. （她比我想的年轻）噢