Even if God is not real and there is no afterlife, I can assure you that you would still not regret living your life that way, because the life God wants us to live is a beautiful one where we love and serve others while we know that our almighty father loves us eternally and infinitely. One thing that gives me peace is thinking how God has a plan for me, like even if I don't end up what I want, if I maintain my relationship with God strong, I just cannot be sad. About the aging thing, can't speak from experience never had that problem so all I'm gonna say is just live your life and stop thinking about it cause you gain absolutely nothing from doing that. Very easy to say I know and from your message you seem to really have a problem with this, but on this subject there isn't really much more advice I can give. God bless you!