Yes, Mel Gibson did appear in Tim, which was released in 1979.He played the role of Tim Melville.
Mel Gibson
Mel Gibson was the director of the movie The Passion of the Christ.
Signs
In no movie was Mel Gibson an Irish hero. You may be thinking of William Wallace; the SCOTTISH hero he portrayed in the movie Braveheart.
Mel Gibson
Mel Gibson played the role of a chauvinistic advertising executive in the movie What Women Want.
I think you may be wanting the movie "Tim' starring Mel Gibson, Piper Laurie plays the older woman, it was Mel's first big role if memory serves me.
This does sound like an early Mel Gibson film called "Tim" (1979) in which Mel Gibson plays Tim the gardener, who is mentally childlike. But the female lead in the film of Mary Horton, was played by Piper Laurie, an older lady who fell in love with, and married Tim, which caused problems within his family.
Maverick and The Beaver
it is 'Passion of the Christ'
Chicken Run