"She will come to your age" sounds a bit awkward. Maybe something like "When she turns your age" or even "When she turns 40" would work better so that it doesn't sound ambiguous.
After that you could say "you may/might have already died" though I would prefer "you may/might already be dead".
So your full sentence could be:
"When she turns 40, you may/might already be dead."
Other ways to say this same thing are:
"By the time she turns 40, you may already be dead."
"You may be dead by the time she turns 40."
In essence, I think the "have" is awkward and there are better ways to get your intentions across. Adding "already" helps buffer that.
I would have preferred to ask questions in the comments but I don't have the rep. I'm by no means an English expert - just your average native speaker - so take this with a grain of salt.
Looking @SovereignSun's answer will give you more technical reasoning that I couldn't give you.