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It won't hurt to link from older articles, but I'd take a look at what kind of Page Authority / PageRank these older articles have before bothering. If new posts, without generating any new backlinks from external sites, are ending up with about the same authority as those old articles, new/old probably won't make much difference. One thing you might want to bring into consideration is the level of traffic, and through what keywords, those old posts are getting - if they're on related topics to the pages you're trying to rank, you can channel some relevant traffic to these pages while you're building the links by creating some more visual emphasis (instead of just linking some anchor text within the post, use a call-out box to entice some clicks). There are a lot of unknowns from my standpoint, but that's my advice based on what you've described.