On the official website it used to mention this that the result of the medical exam is valid for 12 months and that the results of the exam must be valid for at least 6 months at the time of submission of application for permanent residence. Now when I go to the same link, it's not there anymore so I'm assuming you can use your 7 months old medical exam.
I know for sure that it used to mention "..must be valid for at least 6 months.." because I actually created an LOE citing this "at least 6 month validity" statement from the official website to explain my case where at the time of my submission of application, my medical was cutting it very close to the 6 month mark. My advice would be to undergo another medical if you can. If you can't, since there's no official mention on the website anymore regarding the 6 month validity, you can go ahead and use your 7 month old medical exam.