Tosefta su Yoma 7:6

Kohanim that reach puberty, and even when they grow old, are fit [to perform the Temple service], but a blemish renders them unfit. Levites from 30 to 50 years old are fit [to perform their duties], but a blemish does not render them unfit, and consequently it is said (Hul. 1:6), "[What is] fit for a Kohen is unfit for a Levite, [and what is] fit for a Levite is unfit for a Kohen." In what case does this apply? In the Tent of Meeting in the desert, but in the eternal House (i.e., the Temple), the Levites are only rendered unfit as to their voice (i.e., participating in the Levitical chorus). [What is] fit in the Kohen Gadol is unfit for an ordinary Kohen, [and what is] fit for an ordinary Kohen is unfit for a Kohen Gadol. [What is] valid in the golden vestments is invalid in the white vestments, [and what is] valid in the white vestments is invalid in the golden vestments (see Yoma 7:4).