The simple answer is: No. You might not have to wait at all. You should probably discuss this with a vocations director of the diocese or order you are interested in. They can help prepare you and if they judge you to be suitable and have been speaking with you for a while they may make the decision that you could attend seminary or novitiate more quickly.
Many religious orders have a stage before you become a Novice. During this stage, postulancy, you live the life of a religious brother but you make no commitment to the order. This could, in theory, be done even if you aren’t baptised in the Church.
I would recommend speaking to a vocations director now if you are interested in priesthood.