There is some very good advice written above by some very experienced and knowledgable dog folk, BUT i'm inclined to say the exact oppisate of them.
First do u want a deer dog that also picks game or a gundog that also tracks deer. Do u do far more days picking up than stalking?
And wot standard do u want ur dog to achieve at each discipline
I have always been told train ur dog to do wot u want it to do most and best and then when its switched onto that u can add the next discipline. There is no doubt a good experienced trainer (and not trying to say ur not a good trainer
) could easily train a dog to do both but to lesser mortals ur possibly making it very easy to confuse the dog when working it later as Jimmy said earlier on.
I personally would prob train ur older dog, 7's not that old and not entirely different from following a runner, u prob won't get it to the same standard u would a pup, but it should still be a perfectly capable deer dog. I'm guessing u also have a dog around 4ish? i'd then start training that and try and learn and improve from the mistakes u made on the older 1 so by the time ur pup's figured out and experienced the gundog bit u will have already trained 2 deer dogs so will have more idea and make it even better. For me tracking is a natural progression from gundog work (jist an extension of following runners really) whereas i would not say gundog work is as natural follow on from tracking.
I have a young GWP that i have no intention of doing any deer training (but very basic) with until he's really figured out the pointing side and experienced, prob 4 or 5. Any of my other dogs will track fresh shot deer to (to a standard i'm happy with for the stalking i do) which is all i need. And i understand it won't get to the same standard of tracking as if i trained it as a pup but it will still be far more than capable off fufilling my needs.
That probably won't help u as aggainst wot everyone else has said; but it will give u a different point of view and different opinion. Not saying it's right but wot i'd do.
Best off luck to u