old cubase on new christmas gift pc for father

my father is a musician not me. so i do not know a lot about cubase and how it works. his old pc died about a year and a half ago so i have saved up all year to get him a new pc. sadly we do not have the money for the newest cubase.
so im installing his old cubase on the new pc.
he had cubase 5 with the dongal.
right before his old pc died he had ordered a cubase control key pad used from ebay. it surprisingly came with cubase 7 install disc apparently the old user had upgraded to cubase 8 and was getting rid of his 7.

it did not come with a dongal for the licencing though. it did come with a activation key
so my question for those that know is if i install 7 can i use the 7 activation key and use the dongal that came with 5?
or should i upgrade 5 to 7 using the disc? or is he stuck with 5 unless he pays the $500 for the newest one?
we realy don’t have that kind of money and we might never have it so I’m just trying to set him up with the best he can have with the money we have.

thanks for any help you can give if you think i should move this post to another section of the forum please tell me.