1. The next few years, you are growing in and out.
2. Over the next few years, you are growing in and out.
3. In the next few years, you are growing in and out.
4. During the next few years, you are growing in and out.
(Which one is correct? Which one is a common expression? Is a preposition missing in #1?)
First, since you are talking about the future, you need to use a future verb tense... will be growing.
Second. growing in and out...doesn't make sense. Do you mean taller, bigger ?