So, we know that in Avengers: Endgame
Steve decided to stay in the past to grow old with Peggy, thus making the choice to bypass his time stamp and, as a result, grow old.
In the few moments before he
Went back in time to return the Stones,
Bucky tells Cap:
"I'll miss you buddy," and Steve replies: "Try not to do anything stupid while I'm gone." At that moment Sam asks "How long will this take?" and Bruce replies (something like): "For us, 5 seconds. For him, as long as he needs to return the Stones."
I'm assuming here that Bucky didn't know that, until Bruce explicitly said so, that it would take only 5 seconds for Steve to get back. I'll miss you buddy would make a lot of sense if Bucky thought Steve would take days/weeks to get back (he has to return the Soul Stone to Vormir [somehow]). His look of surprise at seeing old Steve at first also made me wonder. (Though, who wouldn't be at least a little bit surprised seeing your best friend age 30 years in a matter of seconds?)
So my question is:
Do we actually know if Bucky already knew what Steve was going to do at the end, as (seemingly) implied by the narrative?