“By this time next year, I will have been collecting football memorabilia for almost 20 years” is the correct sentence.
In this sentence we are using the Future Perfect Continuous tense which is used to show that something will occur up until a certain point, therefore you will have been collecting memorabilia until “this time next year”.
The Future Perfect Continuous tense is a great way to talk about an action that stated in the past and will continue to occur until a specific time or event in the future.
- He will have been working for ten hours by the time his replacement arrives.
- They will have been travelling for one month when their friend comes to meet them.
- George will have been studying medicine in college for five years by the time his sister starts studying pharmacy in the same college.
- How long will the police have been conducting interviews before the lawyers arrive?