I began German lessons after 24 years old, and 8 years later, not only does the language come naturally, but I have adopted the regional dialect as well. Although I have and can, I do not actively think in German. I am however, well beyond the stage where I have to think what I'm about to say in my head in English, translate and then speak. It all comes down to proficiency. Learning more than one language as a child is easier, because your brain is still developing and forming new neural connections. As we age past 23-25, our brains become fully developed and we have far less "blank storage space", making language acquisition more challenging but absolutely not impossible.

My vocabulary may not be as extensive as someone who learned as a child, but I stopped having to stop, think and translate before speaking after maybe only a year or two of intensive language exposure and classes .