Just ask; you're often expected or even required to take a portion of your vacation days within the year you earn them (in the US/UK anyway). Asking for vacation 7 days after starting would be a little awkward. After 7 months, probably not.
If you're concerned about how it looks, check with your boss that the time is okay. Check your department calendar first to make sure you're not asking when half the department is off.
Your only concerns here should be:
1. Do I have days I can take off?
2. Can I do it without disrupting my department more than necessary?
I was in about this exact situation, but it was pretty obvious taking vacation in your first year was okay; we actually are only able to carry over up to 3 days of vacation time, so I had to take those vacation days! Ask your Payroll or Human Resources department for what their policy of that is.
Bottom line is, if HR/Payroll gave you vacation days, they gave you them for a reason. Any good manager understands that time off is important for productivity, and that's not only true for those who have been at the company for a long time.