If you're looking to get into production, writing, acting, or anything related to the creative area of entertainment, this job will feel like hell, you'll be unsatisfied with your position most of the time, and it'll usually only serve getting you into another entry-level area of entertainment regarding the creative side. And that's only if you remain here as an assistant for at least one year.
As stated above, this job only really is fully fruitful if your career goals are in entertainment business or repping clients. And if it is, prepare for a life-consuming career.
This path is for those who actually like to work 60-70+ hours a week, and you won't yield well if you don't, unless you're established and have clients like De Niro. Though it'll take at least a decade to secure clients of that caliber, and again: that's only if you're good at what you do.