link benefit ages on a sliding scale based on how long the link has been in place (also lots of other elements like page content, number of new links/page rank going to the page etc. But generally older links are worth more if the site is a live site .
I wouldn't rotate links over 90 days, it is a pointless short term exercise and can only really serve to let Google know that your links are subject to change, so your site is a short term popular site.
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