The rules of Hinduism are clear on the issue of paying respects to the wife of an elder family member, even if the lady is younger in age....
In Ramayanam, Lakshmana is younger to Rama by just two days.. Even though it is not clearly stated in the epic , Sita is presumed to be younger to Rama younger and therefore youngerto Lakshmana too... Laksjmana was born just two days after Ram ..
Rama on the Star Punartham of Chitram and Lakshmana with his twin Shatrughna on the next Aashlesha or AAyilyam star..
And there is an occasion in Valmiki Ramayanam, where, Lakshmana is asked to identify the jewellery thrown down by Sita in Rishyamooka while she was being abducted to Lanka by Ravana..
नाहं जानामि केयूरे नाहं जानामि कुण्डले नूपुरे तु अभिजानामि नित्यं पाद्दभिवन्दनात I
Naaham jaanaami keyoorey naaham jaanaami kundaley noopurey tu abhijaanaami nityam paadaabhivandanaat....
"I do not know how the ear-studs or the armlets of Sita would look like but I do recognize the anklets worn on her legs,, as I do see them when I prostrate on her feet every day.."
Here Lakshmana, by all means is elder in age to Sita.. but Sita is his elder brother's wife. and therefore he worships her feet..
Dharmasastras equate elder brother to ones own father and elder brother's wife to one's own mother..
Just as, if one's father marries a lady younger to the person, she assumes the status of mother. even if she is younger in age.