To solve this problem, let's analyze the sets $A$ and $B$ and their union step by step.

1. **Understanding Set $A$:** The set $A$ is defined as $A=\{x | x < 2\}$. This means $A$ includes all real numbers that are less than 2.

2. **Understanding Set $B$:** The set $B$ is defined as $B=\{x | 1 < x < 7\}$. This means $B$ includes all real numbers that are greater than 1 and less than 7.

3. **Finding the Union $A\cup B$:** The union of sets $A$ and $B$, denoted as $A\cup B$, includes all elements that are in $A$, in $B$, or in both. Given the definitions of $A$ and $B$, the union will include:
- All numbers less than 2 (from $A$)
- All numbers greater than 1 and less than 7 (from $B$)

Combining these, we see that $A\cup B$ includes all numbers less than 7, since it encompasses both the range of $A$ and the range of $B$. Therefore, we can express the union as $A\cup B=\{x | x < 7\}$.

Hence, the correct answer is $\boxed{A}$.