As a rule, the front three speakers should match. That's to say from the same manufacture/line and era. The two surrounds are not that critical.
Now, do your current "3" speakers match that criteria? If so, then these new speakers would make great surrounds.
If not, well, then you need to decide which direction you want to go.
But, as far as component age goes, I'm currently enjoying a pair of 38 year-old JBL L-26 speakers being driven by a 40 year-old Marantz 2230 playing classic rock on FM.