[edwin hubble]

Well, yes... memes would die out as the user-population dies. (We will see some of this as Europeans fail to replace themselves.)
But then memes (and religions) can grow exponentially During a human lifetime.(Christianity, Islam)

[BMCDA]

Sure, It depends on how convincing a new idea is and some can spread like a bush fire. Nevertheless it's a fact that older people are generally harder to convince because they cling firmer to their preconceived beliefs.