I'd find it strange that you can only become senior after X amount of years. Some people are just more skilled than others. One person can do a job for 20 years and still only be medicore, whereas others could do a job for 1 year and be a master at it.
I would assume the title is based on merit and ability, not X number of years regardless of how good or not they are.
I would assume the title is based on merit and ability, not X number of years regardless of how good or not they are.