Informix? Definite LOL. :p Must have been Vodafone, right?
Imo, best way to get into it is to keep going with your development, pick up some DB admin experience in Oracle or a decent relational database and ask the current DBAs lots of questions. Always query the SQL you write for efficiency! Learn how to write PL/SQL.
Perhaps look into doing the Oracle developer exams in your spare time?
And then get a position at a company where there is possibility of moving into that field. Where I work, developers often design their own database schemas, set them up and do some degree of optimisation for smaller projects. You can pick up a lot of the basics this way, especially if you;re interested in learning how to improve things. Making a transition into a more senior DBA from there wouldn't be too difficult, given the right enthusiasm and training.