Can we use might have for future possibility?

Question

I know that we use might have to show that something has possibly happened now or happened at some time in the past. But can we use it for future? For example:

Just imagine there is a person who is 40 years old and he loves a girl who is 18 years old... For teasing him I say:

"You are too old, when she will come to your age you might have died"

Is it a correct sentence? I don't know...I'm a learner, please help.

Answer 1

"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."

or

"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.

Answer 2

"might have + past participle" is used only in the past and present:

• I might have said something bad.
• I might have been given this letter but I don't remember.
• They might have come already.

In the future we can either use "might + present participle":

• Tomorrow I might be at home.
• In an hour I might leave.

Or "might + have to + present participle":

• In half an hour I might have to leave.
• She might have to take her papers with her today.

Nothing like "will might" or "will might have to" is possible.

So your sentence can be:

• You might be dead by the time time she turns 40.

Answer 3

"when she will come to your age" is incorrect. When she gets to your age, when she is your age, are both acceptable, although in this context, for clarity, you might want to say, when she is the age you are now or when she get to the age you are now.

I don't know of any instance in English where we would refer to age as something you come to, unless you are saying that someone comes of age, which is very different. You are an age and you get to an age, but you don't come to it.