How long will it be since our parents got married next year?

To determine how long it will be since the parents got married next year, one must consider the current year and the number of years since the marriage occurred. If the answer is 25 years, it likely means that this year marks the 24th anniversary of their marriage, and thus, next year would be the 25th anniversary.

This conclusion is based on the general pattern of how anniversaries are calculated in relation to the current date and future calculations. The other answers do not align with this logic, either suggesting a duration that is too short or too long when considering the typical timeframe for marriage anniversaries.

Therefore, arriving at 25 years as the eldest age of the marriage next year reflects a coherent understanding of how anniversaries are counted and the context in which the question is framed.