Looking for a movie from childhood 80-90s

No idea about the plot, what I remember is still vivid in a way with certain meaning.

The movie had a major plot which was a romance between a man and a woman, cool looking girl maybe 25-35 years old. The man was actually a little boy somewhere around 11-13 years old, who somehow i think transformed himself temporary to be an older man, either some magic or technology, after doing that he met that woman and fall in love with her and she fall in love with him. At the end of the movie, she had an option to also use that machine or something which she did, and turned herself into young girl, so she could be with him.

The movie ain’t Big from 1988, most likely is 90s movie. The main theme was something that the young boy needed to do that is why he turned himself temporary old, but no idea what it was. Meeting that woman and fall in love was in between that and it worked in the end with happy ending, giving them more time to be together, as she became young too and full life was ahead of them.