[exim] Outofdate email

Greetings

Me again (c:}

I often receive email that is a few days / months / years "old"
according to the email date 99.99% of which is SPAM.

Now a thought, what would the benefit/negative be in denying
incoming email "older" than say 7 days? I was thinking that denying
at connection time would alleviate load on SpamAssasin (my resources
are limited on a VPS).

Any ideas on how best to do this? Pointers / examples greatly
appreciated as always.

Regards
Michael