In terms of getting a title of "Senior Engineer" at most companies, it is mostly a function of experience. It is highly unlikely you will be hired as a Senior Engineer straight out of college.

Don't focus on getting the title. Instead, focus on what you can control, and the titles and career advancement will take care of themselves.

There's a well-known, well-written essay on the qualities that a Senior Engineer possesses: http://www.kitchensoap.com/2012/10/25/on-being-a-senior-engi...

Technical maturity comes from working on and finishing large projects. As with anything else, you can work for years and have lots of "experience", but if you are not critically thinking and learning during the journey, you won't get anywhere. Learn the pros and cons of high-level, architectural decisions so that you can be prepared to make those decisions someday in the face of uncertainty.

Personal maturity means working effectively on your own and especially with others. Pay attention to the highly respected engineers in your organization, and observe how they work with others.

Good luck!