3 sentences

1. 他们的年纪相仿。

   tā​men de nián​jì xiāng​fǎng.

   They are of a similar age.

   Source: Dong Chinese Dictionary

2. 他们年龄相仿。

   tā​men nián​líng xiāng​fǎng.

   They are about the same age.

   Source: Tatoeba

3. 他年纪和你相仿，，她却和我差不多大。

   tā nián​jì hé nǐ xiāng​fǎng,, tā què hé wǒ chà​bu​duō dà.

   He's your age, and she's about my age.

   Source: OpenSubtitles