You can apply for Estonian e-Residency online here.
Please note that you are required to collect your e-Residency digital identity card in person from one of the pickup locations or the Police and Border Guard Board service points in Estonia. If you cannot travel to any of the pickup locations you should not apply for the e-residency.
Underaged persons can apply for the e-residency card but their digital signature is not considered to be legally valid in Estonia and they cannot serve as board members of Estonian companies.
This means that registering a company while being less than 18 years old is not possible via Unicount.