I believe he's saying that he had fresh strawberry preserves readily available as a child; however as an adult that was not the case. He didn't come to realize how fortunate he was to have the strawberry preserves until adulthood.

There's a saying "you don't realize what you have until it's gone." People tend to take for granted the most precious things (and people) in their lives. When they lose them, they truly feel the pain of what they're now missing.

Maybe OP regarded them as too common when he was a kid, and only realized as an adult how much of a treat they were.

Strawberry preserves are so easy to make though. The benefit being you can add much less sugar than the store bought.