All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Allaah, the Exalted, has clarified to us in His Book the Mahaarim (non-marriageable relatives) of a man, either from the family lineage, or by suckling relationship or by marriage. So, if this man is not a Mahram to you by one of the above means, then he is a marriageable man to you even if he was the one who nurtured you and educated you, and is elderly. All of this is not an excuse of unveiling in front of him. If you unveil yourselves to him, you are sinful.
Allaah Knows best.