Hi. I don't live there but my boyfriend does, so I'm up there every other weekend!
His address is Harrisburg, but he actually lives close to Hershey Park in an area called Manada Hills. Its about a 15 minute drive to the city itself. It's a very nice area, but not sure how fun it would be for a single 20-something. I would suggest looking at areas closer to the city. I think 2nd Street is where all the fun happens.. Bars, restaurants, ect.
If you like seafood I very highly recommend a visit to the Devon Seafood Grille in Hershey!!
And the Hershey Pantry for breakfast-- but not on a weekend during the summer when it's mobbed with all the families visiting the Park!!
There is a very fun bar in Mechanicsburg called Buck Wilds. They have live music and a mechanical bull!