Are ages calculated according to the Hijri or Gregorian calendar when determining the age for teaching a child to pray, as in the saying of the Prophet, peace and blessings be upon him: "Command your children to pray when they are seven years old"?

The lunar years are what is considered in Shar'i (Islamic legal) delimitations, due to the statement of Ibn Taymiyyah regarding the verse (They ask you about the new moons): "Allah made the new moons time-markers for people in judgments established by the Shari'ah from the outset, or as a cause for worship, and for judgments that are established by the conditions of the servant. So whatever is established of time-bound matters by Shari'ah or condition, the crescent moon is its time-marker. This includes fasting, Hajj, the period of ila' (oath of abstinence from wife), 'iddah (definition) (waiting period), and expiatory fasting." And due to the statement of Al-Shalabi in his commentary on "Tabyeen Al-Haqa'iq": "The people of Shari'ah only recognize months and years by the new moons. So, if they use the term 'year' without qualification, it refers to that, unless they explicitly state otherwise."