Federico, a few versions ago the Account Type feature was completely redesigned and associated with the Roles feature. Many changes have been implemented in the software core code and also it was decided not to show the Account Type on the User Profile Page. And if you want to display it again, this is considered as a custom code modification. But I cannot give you the step-by-step instructions on how to make this modification. You can post it in the custom code modification forum, probably some community member already have a solution.

But It would be much better to do this via creating a plugin.
if you don't have programming skills you can find a third-party developer here: http://www.oxwall.org/market/specialists.

Or if you sure that this new functionality is essential for all oxwall users, then feel free to submit your idea at Oxwall uservoice to set it priority higher. You can do it here:  http://oxwall.uservoice.com/forums/13756-ideas-for-oxwall.

Tnx Taissa, i like your advices. I'll try, but if you are so kindly to tell me where i can found the code section to change, i'll owe you.  

Federico, I'll PM you an example.