PostgreSQL Why where does not work with age function : I use age function in where but i don't know why it dose not work 

```
select t1.id,date_part('year',age(t1.tdate,t2.birthday)) as age
FROM table t1
LEFT JOIN table2 t2 ON t1.id = t1.id
WHERE date_part('year',age(t1.tdate,t2.birthday))  >= 10
```

￼￼￼￼the result is incorrect 
-----------------
![the result][1]
[1]: https://i.imgur.com/WeRPAqa.jpg "result"
<br/>
￼￼￼￼the result should be  <br/>
-----------------

![the result][2]
[2]: https://i.imgur.com/pPvzcvA.jpg "result"