What do you think will be your greatest challenge as a young business professional?

Myself being just that, it is three fold:

1. Being taken seriously in any situation
2. Dealing with those who do take you seriously but use your age as a way to manipulate you and others in a business relationship.
3. Getting over the fact that once you become a good business man, age does not mean anything.
All three can be handled by acting like a businessman and not of any particular age. Personally I've been able to use my age as a benefit by better understanding the technology markets and consumers.

I worked for a company who had a CTO that said he wanted everyone to have 9 inch screens with 2jiga of drive. This was in 2008. =0