I'd say go on out! Have fun! It's just a date. Of course it's not easy getting over someone you've been with for so long, but you need things in your life that make you feel good and valued.
I had a very hard time initially after my ex broke up with me after 3 1/2 years of being together. I had my ups and downs for about the first year. I found out that he got married to someone about a year and a half after our break up. I was in total shock at first. Cried thinking that was suppose to be me blah, blah, blah. But then I was over it. I've been single going on almost 4 years now. I've been dating here and there, but haven't really connected with anyone. I don't think you can really put a time for how long is enough before starting another relationship. Some may need longer than others. Do things for yourself for time being.
For the most part people do need time to heal before jumping right into another situation, but going out on a casual date isn't a commitment! Life is too short! Enjoy it! :)