One of the most important things to do with a backlog is groom it. You should go thoughthrough the backlog and prioritize the tasks.
It can seem overwhelming when the backlog grows faster then it gets cleared but understand the backlog isn't simply a to do-do list. It's a documented record of how critical the proposed work is. Simply being in the backlog is not a promise that it will ever be resolved. Sometimes it'sthe backlogs job is to remind us that we've seen an issue before and decided it's not critical.
Focus on that. It shouldn't matter how old an issue is. Just how much we care about it.