Hearing aids are small sound amplifiers placed in or on the ear for partially deaf persons. Hearing loss greatly effects the elderly, 72% of those suffering from hearing loss are above the age of 45. Thats why you may find a good portion of elderly wearing hearing aids.
My grandma started using a hearing aid about a year ago and still is having trouble hearing or deciphering sounds from voices. I never really understood why it is so easy for someone without hearing loss and a hearing aid to pick out voices from sound easily while someone with hearing loss using a hearing aid will have great difficulty at it. I had found that modern hearing aids are digital- they convert sound picked up into digital messages, use algorithms to separate frequency regions to amplify selectively. Older hearing aids amplified all sounds equally, but the newer ones will amplify only sound frequencies in the human voice range.
I didn't find any confirming evidence, but I would guess that my grandma sometimes has issues deciphering noise and voices because some noises have the same frequencies as the human voice and so is also amplified to a distracting level. I think that as technology advances software will become more equipped at recognizing human voice.