Foreigners often make some strange mistakes in Chinese when they study the most difficult language--- ---Chinese. We try to analyze typical sentences to correct these errors.

         Lǎo nǎinɑi, nín jīnnián jǐsuì le?
False: 老奶奶，您今年几岁了？
         Lǎo nǎinɑi, nín jīnnián duōdà suìshù(nián jì)le?
True: 老奶奶，您今年多大岁数（年纪）了？

“几岁”使用场合不当，在汉语里，询问老人年龄时，要用“多大岁数”或“多大年纪”。问小孩的年龄时才用“几岁”。
The use of 几岁 doesn't fit the context here. In Chinese, to inquire the age of old people, 多大岁数 or 多大年纪 is used. In the case of small children, one should say 几岁.