A rule states that in order to drink beer, one must be over $18$ years old. In a bar, there are $4$ people. $P$ is $16$ years old. $Q$ is $25$ years old. $R$ is drinking milkshake and $S$ is drinking a beer. What must be checked to ensure that the rule is being followed?
1. Only $\text{P’s}$  drink
2. Only $\text{P’s}$  drink and $\text{S’s}$ age
3. Only $\text{S’s}$ age
4. Only $\text{P’s}$  drink, $\text{Q’s}$ drink and $\text{S’s}$ age