I took tetanus diphtheria pertussis vaccine dtap/tdap. i don't remember last when i took this vaccine. maybe when child/teen i'm 21 years old now. i have just read pertussis vaccine should not be taken before 10 years of last dose. is there any risk?

In a word, no. Taking the pertussis vaccine early is generally safe. At 21 years of age most young people are due for a booster but it would cause no harm to receive the vaccine early.

Keep vaccines current and review your records with your physician. A booster may be provided and at your age, it is reasonable to obtain a booster. Antibody testing is available to confirm the presence of protective antibodies.