As I am still in my 20's and actively looking for opportunities that seem endless to me, the greatest challenges in terms of mindset for my career would most probably be when you see people older but are way more stable in life (in other words patience) a lot of people need to know that it is not even a matter of age , it is just a matter of perseverance and patience to get to the point you need in life, other than that .. as someone who has Adhd, it is very hard to keep the beginning's motivation , so what's more needed is discipline in terms of mindset.. that's going to go a long way if you were disciplined and patient enough.. but the catch is that it's not just that.. You got to ALSO be passionate about whatever it is you want to do, and be able to take risks as well.
This in my humble opinion are the greatest challenges in term of mindset for anyone and any career.