What is some good advice on how to cope with ...when people (older) telling you that things might not work out (ie; your job, relationships, etc) because they think they have more experience than you?

I'd respectfully thank them for their "advice" or opinion and tell them not every situation is the same. Their may have turned out differently, but in this situation there different factors and personalities etc, to apply. Making every situation impossible to turn out EXACTLY the same.. its just not possible, maybe similar but yeah. Things can change, and having the experience for yourself matters as well, as you're experiencing it..

What do you want to know? Ask me! :)