Endorsement and 18 years above age restriction is first things that needs to be checked. Other requirements are:

• Have a minimum level of English Language at least CEFR level B2 in reading, writing, speaking and listening. However, if you are applying within the United Kingdom and have already proved your knowledge of English language to be of level B2 in any earlier successful application, then you are exempt of this requirement. Moreover, if you are a national of English-speaking country then you are exempt of this requirement.
• Be able to maintain yourself while you are in the UK. You need to have at least £945 in your bank account for 90 consecutive days before you apply. (If you are applying from outside the uk, and the maintenance funds are held in another currency. The amount of maintenance funds will be converted using the GBP exchange rate. The Home office relies upon oanda for exchange rates).

You can apply for a Start-up visa if:

• You want to set up a business in the UK.
• You’re from outside the European Economic Area (EEA) and Switzerland.
• You are at least 18 years old.
• You meet the English language requirement.
• You are able to prove that you have enough personal savings to support yourself while you’re in the UK
• You must get your business idea endorsed by an authorized body that is either a UK higher education institution or a business organization with a history of supporting UK entrepreneurs.