(1) If you returned home from Makkah before sighting the moon of Eid Al-Fitr then hajj was not fardh on you. However, if Shawwal started and you were in Makkah and you had the expenses of Hajj then hajj became fardh. If the government does not allow to stay there then there is difference of opinion among Ulama whether the hajj was fardh or not. As per some Muftis it is preferred that hajj becomes fardh when Shawwal starts in this case and if one is unable to do it oneself then it is fardh to send someone for Hajj-e- Badal though one sends some pious person from Makkah. If one has the capacity then one should perform hajj again from one’s country. So it is mentioned in Ahsanul Fatawa Vol. 4, p. 529.
(2) There is no age limit in Hajj Nafl. However if it is fardh hajj then it should be performed by an adult. It is not a condition to be married.
(3) If you are capable to do hajj now then it is fardh on you.
Allah knows Best!
Darul Uloom Deoband