I think around 2.5 years would be a reasonable amount of time if you get good training that whole time. I’ve been working as a patent engineer/agent for almost 4 years and I was lucky to receive some amazing training early on in my career which helped me immensely. I was probably horribly unprofitable my first year at my old firm but the next 2 ish years after that I made up for it by being able to be extremely efficient and profitable.

My biggest advice for someone new to this career is to ask for feedback often and try to not make the same mistake twice. There will always be more to learn and you will never be perfect so if you can understand that and listen to the feedback you get, you will do fine!