In order to be SEIS eligible, the company must have been trading for less than 2 years.
There is no clear definition of trading aside from the general observation that it would involve “undertaking activities with a view to a profit”. HMRC use the analogy of a shop: if you have something on the shelf that someone could buy even if they don’t, you can turn the sign to ‘Open’ and that’s you trading.
Note that trading is not incorporation or the raising of funds nor is it your first commercial sale.
You can see our complete article on this here: What is Trading for SEIS