Robertson is enjoying his involvement as Scotland prepare for Wednesday's friendly with Poland in the National Stadium in Warsaw.
This time last year Robertson was playing for Queen's Park against the minnows of Scottish football in the country's bottom league.
But following a summer move to Tannadice, the 19-year-old has blossomed under United manager Jackie McNamara.
Robertson admits his Scotland call-up has been a surprise, and while he has faith in his ability, the youngster did not envisage such a rapid rise from playing in a 2-1 defeat to Montrose this time last year.
"I actually remember that game well, we played terrible," Robertson said. "Nobody could have imagined how quick I have progressed, but I wouldn't want it any other way. You learn things so quickly.
"It's been a quick progression but I always knew I could do it. It was just about getting a chance. Luckily the gaffer at United gave me the chance and I think I have repaid him."
Robertson also caught the attention of Scotland boss Gordon Strachan when he was called into the U21 squad, and he joined the senior pool at a training session ahead of last year's match with Croatia.
"It was brilliant, training with players who were playing in the top leagues," Robertson added. "That helped a lot and showed the standard you have got to be at.
"You were there to try and enjoy it. You knew you had no pressure on you because none of us were in the squad for the Croatia game. It was just the boys that hadn't played.
"But Gordon takes quite a lot of interest in training and that's probably why I'm here, because I did do well in training. Obviously my performances from United have been good enough."