First of all the whole IQ system was developed in 1904, and many dispute whether it actually has any bearing on a persons intelligence.
Second, your IQ stays the same no matter what age you are. I was tested at age 8, 15, and 25 with the same results ranging between 160-170, but the test must be done by a professional (not online) because the tests factor in much more than just your answers, but also your demographics and other current statistics.
If you really want to know, arrange to take a formal test through Mensa. I was a member and enjoyed their activities, but do yourself a favor and don't go around telling people what your IQ is...it always rubs people the wrong way, and probably means nothing at all (other than you may have a higher potential for intelligence with a proper education and training).