I agree with Steve. MCI is not the same as dementia. We all age and decline with that age. People are too quick to throw out the labels of dementia and Alzheimer's though, without a medical diagnosis.

Here's some signs of dementia:

Cognitive: mental decline, confusion in the evening hours, disorientation, inability to speak or understand language, making things up, mental confusion, or inability to recognize common things
Behavioral: irritability, personality changes, restlessness, lack of restraint, or wandering and getting lost
Mood: anxiety, loneliness, mood swings, or nervousness
Psychological: depression, hallucination, or paranoia
Muscular: inability to combine muscle movements or unsteady walking
Also common: memory loss, falling, jumbled speech, or sleep disorder

Biden does have some speech fumbles, hence the MCI (mild cognitive impairment). He also has a history of having a stutter, so ... It makes a kind a sense that he'd struggle with speech again in old age.

The speech impairment is the only one on this list I've seen any real evidence of. I know he hurt his leg, playing with his dog but for the most part he's pretty steady on his feet. He doesn't seem to have any of the behavioral markers that were so obvious in Reagan and Trump either.

True dementia only affects a relatively small percentage of the elderly.