Four people $\mathrm{P}, \mathrm{Q}, \mathrm{R}$, and $\mathrm{S}$, of different ages, make the following observations.
- $\mathrm{I}$ am younger than $\mathrm{S}$.
- $\mathrm{I}$ am neither the youngest nor the oldest.
- $\mathrm{P}$ is older than me.
Based on these observations, the youngest person is $\_\_\_\_$ .
- $\mathrm{P}$
- $\mathrm{Q}$
- $\mathrm{R}$
- $\mathrm{S}$