A distribution from your Roth 401(k) made before you reach age 59½ is not a qualified distribution regardless of how long you have had the account.
Distributions from a Roth 401(k) are a prorated mix of original contributions and earnings. The portion that is a return of your original contributions is not taxable. Since you will be age 55 when you leave the job, the portion that is earnings in any distribution that you make from this employer's Roth 401(k) after leaving the job but before you reach age 59½ will be subject to ordinary income tax, but will not be subject to an early-distribution penalty. The distribution will qualify for the age-55 penalty exception.
After you reach age 59½, since it will be more than 5 years since the beginning of the year in which you first made a contribution to this Roth IRA, any distributions will then be qualified distributions, entirely tax and penalty free.