Demographic details like age, gender, location, job title, and marital status are the bare necessities of any persona. They briefly introduce your users and evoke some empathy even at an early stage. Your website/app analytics can be the perfect source of demographic data. However, not all data might be relevant to your product. For example, marital status, occupation, and income are helpful for a banking app but have little value for an English learning website. So, make sure you mention this data for a reason.

A word of caution — don't use demographic data as the only source for creating personas. It's a strategy that works only for market segmentation goals. Avoid making assumptions about users' needs and pains based on age, gender, race, and income, and build your personas on research insights.