Praise be to Allah.
We share your fears concerning marriage to this man, and we urge you to agree to marry a man who is religiously committed and of good character if one comes and proposes to you, because the Prophet (peace and blessings of Allaah be upon him) said: “If there comes to you one with whose religious commitment and character you are pleased, then marry (your female relative under your care) to him, for if you do not do that there will be tribulation in the land and great mischief.”
The decision mentioned in the question to get married after five years is strange, but so long as your relative has chosen this lengthy period, you have plenty of time to find someone else who is more suitable, if such a one should come and propose – so long as there is no marriage contract (nikaah) between you and your relative. If no one who is more suitable comes along during this time, it is permissible for you to marry him (your relative), so long as He is a Muslim and he is not doing anything that would put him beyond the pale of Islam. We ask Allaah to give you strength.