Of course, this problem can work both ways. I'm sure there are a good number of aging congregations that have neglected their younger members. Their refusal to adopt new ideas, strategies, etc. basically told the youngest members that they were no longer wanted. Sadly, some churches would rather die than change, but that's a sermon for another day.
Are some churches and denominations pushing the older generation aside? If so, it's nothing new. I'm reminded of a young king named Rehoboam (2 Chron. 10). His father Solomon was a mighty king. Under Solomon's reign, the nation of Israel experienced influence and prosperity like they had rarely ever known.
When Rehoboam assumed his father's throne, he was presented with a proposition - "lighten the burdensome service of your father and his heavy yoke which he put on us, and we will serve you" (10:4). Rehoboam didn't want to make an immediate decision, so he asked for 3 days to consult with some advisers.
Rehoboam had two sets of advisers - young and old. Rehoboam heard from the elders first. They advised him to lighten the people's load and to treat them with grace. Unsatisfied with the wisdom of the elders, Rehoboam turned to "the young men who had grown up with him" (10:8). They encouraged him to double the people's workload by ruling with an iron fist.
What happened? Rehoboam pushed the elders aside, listened to his young friends, and split the nation of Israel in two. The northern tribes took a new king, and Judah was left to fend for itself.
Can we learn something from Rehoboam's mistake? I think we need to learn that God is not done with our elders. Not only does God command us to respect our elders (1 Tim. 5:1-2, 1 Peter 5:5), but we have a great deal to learn from their experience. Paul commanded that the older women were to admonish the younger ones (Titus 2:3-4), but how can we honor that command if the older members are dismissed from our congregations?
If older believers don't feel welcome in your church or denomination, something needs to change. Furthermore, you should invite them back to the table, ask their forgiveness, and seek their wisdom. God never intended us to have "old churches" and "young churches." He's commanded us to grow multi-generational churches for the glory of God until Jesus comes back.