Do you need to wear niqab or hijab infront of elderly non mehram men? References will be great !
In short, yes. A woman must cover in front of elderly non-mahrams.
To expand.. this verse tells us everyone in front of whom a woman may uncover her head:
"And tell the believing women to reduce [some] of their vision and guard their private parts and not expose their adornment except that which [necessarily] appears thereof and to wrap [a portion of] their headcovers over their chests and not expose their adornment except to:
their husbands, their fathers, their husbands' fathers, their sons, their husbands' sons, their brothers, their brothers' sons, their sisters' sons, their women, that which their right hands possess, or those male attendants having no physical desire, or children who are not yet aware of the private aspects of women" -Qur'an 24:31.
From this, we see that women were not given general permission to uncover their heads in front of "elderly non-mahrams". This means yes, you do need to wear Hijab/Niqab in front of elderly non-mahram men also.
The only category of 'elderly men' who the verse does allow a woman to uncover her head in front of is the "male attendants having no physical desire". So eg, an elderly man who is hired by your household who has no sexual desires for women anymore.. around him you'd have permission to take the headcover off. But if he had desires still, then you'd still need to cover.