You said this guy was "your age but a little bit older" How much older? Is he new to town? Does he go to your school? You walked to the park you said right? Could he live in the neighborhood? Maybe you should go back tomorrow with a parent and find out where he lives and if he really has a dog and what his deal is? DO NOT GO MEET HIM ALONE!!! UNDER NO CIRCUMSTANCES!!
I'm trying to think on the bright side here instead of jumping to comclusions about his intentions...maybe he is new to town and trying to make friends before the school year starts? Either way, I am NOT advocating that you meet him or email him back but maybe have your parents or your friend's parents or older brother or something come with you to the park....
If you gave him your email address, perhaps he wasn't so creepy at first? until he started following you!? (THAT is creepy!)