You said you read some posts on the subject, so there is not much I can add but I think if I were you I would not worry about the Missions, but more about the tires being 7 yrs. old.
I know years ago (like 30 to 55) I never cared about the age of the tires as long as they had tread on them. For me back then it was all about the cost of getting new tires.
Back in those days tires were not made as good as they are now. I remember getting flats at least
once a year. Today with my 3 cars & 2 trailers I can not remember when I got a flat last, maybe 20 years ago if that.
I had Missions & put 18,000+ miles on them with NO problems at all.
I just replaced them bacause they were 5 yrs. old, mainly from reading the posts on this site plus cost is not a factor now.
I bought Goodyears Also MADE IN CHINA. I just hope they hold up as well as my old Missions.