Addressing parents as "mommy" and "daddy" is a common practice in many cultures, and there's no specific age limit for when children should stop using these terms. The way adult children refer to their parents can vary depending on their upbringing, cultural background, and personal preferences. What might be considered appropriate or comfortable in one family might differ from another.
In some families, the use of "mommy" and "daddy" may continue into adulthood as a term of endearment or a way to maintain a close, affectionate relationship with their parents. It does not necessarily indicate a lack of maturity or independence on the part of the adult children.
Ultimately, the appropriateness of addressing parents as "mommy" and "daddy" is a subjective matter, and different families have their norms and dynamics. As long as it is mutually acceptable and respectful to both the parents and adult children, there is no reason to be concerned about it. What matters most is the love, respect, and healthy communication that exist within the family, regardless of the terms used for addressing parents.