Are funds earned from a permissible job considered halal if the worker's age is below the minimum age stipulated in the website's terms, given that the work does not involve deception?

As long as the work is permissible, the wage for it is permissible, even if the worker violates a condition regarding age limits. The violation is blameworthy from one perspective, but the wage becomes lawful for him from another perspective because it is a consequence of work that is permissible in itself.