We know that Atticus is an older father because it is mentioned several times in the book, and we know the children are aware of that and of the fact that their family is 'different' because of that. This is difficult for kids at that time of their lives when they are acutely aware of 'fitting in ' with peers. For example, we read in Chapter Ten that
'Atticus was feeble: he was nearly fifty. When Jem and I asked him why he was so old, he said he got started late, which we felt reflected upon his abilities and manliness. He was much older than the parents of our school contemporaries, and there was nothing Jem or I could say about him'
when classmates are comparing Dads. This is relevant for two reasons. Firstly, the children love and respect him despite or even because of this. (The latter because he has a different but wiser method of parenting than many contemporary parents because of all his worldly experience.) Atticus, with all the wisdom of a grandfather, knows that love is all and that children need space to develop and make the odd mistake. He also converses with them in an adult but appropriate fashion. Secondly, we see Scout returning to him again and again for direction and advice (as she does as an adult at the beginning of the novel.) We see that along with racism, agism is also not only wrong but foolish as our elders should be revered for their life knowledge and wisdom.