It would keep that rating unless the producing company resubmits it to the Motion Picture Association of America. Even if resubmitted, it might still keep the same rating.
1988+25 = 2013
Church - the Movie 2013 is rated/received certificates of: USA:Approved
Movie of Nothing - 2013 is rated/received certificates of: USA:Approved
Crackerjack the Movie - 2013 is rated/received certificates of: USA:PG-13
Moshi Monsters The Movie - 2013 is rated/received certificates of: UK:U
American Made Movie - 2013 is rated/received certificates of: USA:G
2013 MTV Movie Awards - 2013 TV is rated/received certificates of: USA:TV-14
Juana C- The Movie - 2013 is rated/received certificates of: Philippines:R-16
Not Another Celebrity Movie - 2013 is rated/received certificates of: Australia:MA15+ (2014)
The Harry Hill Movie - 2013 is rated/received certificates of: Ireland:PG UK:PG
No Ordinary Hero The SuperDeafy Movie - 2013 is rated/received certificates of: USA:PG
You would turn 25 in 2013.