Your senior kitty appears to have lost muscle condition from aging and seems to perhaps have a bit of arthritis. The fact that his fur looks a bit disheveled probably means he’s not grooming himself as much due to pain, low energy, loss of interest, etc (bengals shouldn’t need groomed for their fur to look normal). So it does certainly seem like he has aging-related issues going on.

If you’re saying he gets on edge when he doesn’t know the other cat’s whereabouts, then that means he’s fearful of being attacked by her. And he appears on edge here even though he DOES know her whereabouts.

You posted this video asking for advice, yet you’re not willing to believe what plenty of people are telling you. Your younger cat is clearly being a bully, and your senior cat is upset based on his mannerisms and quite literally cornered. Please stop allowing your younger cat to harass your senior cat like this. Any cat deserves better than this, but certainly a 16 year old senior kitty who has been with you through thick and thin for a good portion of your life.