Is being an older virgin a problem for woman if marrying late? is older vagina not stretchy enough?

No not a problem: If you are menopausal it could make things a bit difficult, a premarital gyn exam and possible estrogen cream to help with vaginal elasticity may be indicated in that case.

Never too late!: If you are not menopausal, it makes no difference what age you are. If you are menopausal, you might need estrogen to normalize the skin lining the vagina.

Not a problem: The vagina can accomodate sexual intercourse with no problem in older age and 50 years is not that old really. A 50 year old will not be able to have children, but there are no limits to sexual activity in that age group.