UPDATE: TheSims.com updated their The Sims 4 Get Together FAQ page with an information about the ESRB rating:
What is The Sims 4 Get Together rated?
The Sims 4 Get Together is rated T for Teen by the ESRB.
Since the announcement, The Sims 4 Get Together’s rating always stated RP (Rating Pending). That means that features that The Sims Team has been working on were still in progress, development and/or creation
Today, The Sims 4 Get Together finally got it’s 12+ PEGI rating, meaning that The Sims Team will no longer work on creating new features for the game. We should expect a real flow of Get Together news starting next week!
Source: EA DE