This study assessed, in a sample of 98 adult native speakers of Dutch, how their lexical skills and their speaking proficiency varied as a function of their age and level of education and profession (EP). Participants, categorized in terms of their age (18-35, 36-50, and 51-76 years old) and the level of their EP (low versus high), were tested on their lexical knowledge, lexical fluency, and lexical memory, and they performed four speaking tasks, differing in genre and formality. Speaking performance was rated in terms of communicative adequacy and in terms of number of words, number of T-units, words per T-unit, content words per T-unit, hesitations per T-unit, and grammatical errors per T-unit. Increasing age affected lexical knowledge positively but lexical fluency and memory negatively. High EP positively affected lexical knowledge and memory but EP did not affect lexical fluency. Communicative adequacy of the responses in the speaking tasks was positively affected by high EP but was not affected by age. It is concluded that, given the large variability in native speakers' language knowledge and skills, studies investigating the question of whether second-language learners can reach native levels of proficiency, should take native-speaker variability into account.