His rise to national prominence has been so swift that he has overtaken many pretenders for a spot in the Scotland ranks and even dislodged those who seemed to have staked a valid claim before him.
The 21-year-old may be restricted to a cameo role against Serbia on Saturday, but his progress is such that one only fully grasps the extent of his youth when he discloses he was just seven the last time the Scottish team reached a major international finals. The 1998 World Cup is but a hazy memory for the Prestwick player, but he has the ability to make an impression on the qualifying stages for the 2014 competition.
Forrest will find it difficult to make the starting line-up for Scotland as Craig Levein weighs caution against adventure and is likely to come down in favour of the former. Robert Snodgrass, James Mackie and Steven Naismith are ahead of the Celtic player in the rankings for a position in a wide area but Forrest has edged ahead of other contenders, most notably Shaun Maloney of Wigan Athletic and Kris Commons, his club team-mate, who has not made the squad for the matches against Serbia and Macedonia.
Maloney, at 29, and Aiden McGeady, the 26-year-old Republic of Ireland winger, were both at Celtic when Forrest was growing up at the club. The Ayrshire lad joined the development programme at Celtic in 2003 and has made giant strides to become an established, influential player for the team. ''I trained with Shaun when I came through the ranks at Celtic. Aiden [McGeady] was there too. Both of them play my position, so watching them and working alongside them was good. I learned a lot from them,'' he said.
Joe Ledley, the Welsh internationalist, believes Forrest has benefited from this education on the playing fields of Barrowfield and Lennoxtown. "I train with James every day and he's a fantastic player – one of the best in the country,'' he said. ''It happened with Aaron Ramsey. We all knew he would become a great player and it's the same with James,'' said Ledley in reference to his fellow Welsh midfielder who now plays for Arsenal. "James is so sharp on the ball but he wants to learn – he wants to get better. You need to be like that and James is a good lad as well. You can see that he can be a fantastic player.''
Asked if Forrest could scale the heights in the same manner as Ramsey and Gareth Bale, the Welsh wide man, Ledley said: ''Ramsey is a different type but James is like Bale. He can take anyone on. His pace is frightening, he's so quick and when he gets going you can't see anyone catching him. But he's also got great technique for a quick winger. He can pick a pass and play it simple. He's up there with the best.''
Forrest has a chance to frank this opinion with performances in the near future. Barring injury, the Scot will be a starter for Celtic in the six Champions League group matches and he will have his chance for Scotland in the qualifying campaign. Levein will be inclined to use the winger as ''an impact sub'' and, perhaps, as a starter when victories are needed rather than merely desired. ''It's an exciting period for me,'' Forrest confirmed. ''You want to play on the big stages. They don't come much bigger than the Champions League and World Cup. I want to try to make an impact at that level.''
Forrest was a protege of Neil Lennon, who coached the player as a youngster. When Lennon became Celtic manager, he immediately moved Forrest up to train with the first team. Manager and team were rewarded with subsequent performances that showed Forrest was a substantial talent.
The winger said: ''I knew that if I kept working hard I would get a chance in the first team at Celtic. Once you get that chance, you need to make the most of it. I've done that so far, but I need to keep going and working hard. That's the key. It does get tougher, but playing alongside the level of players that I do at club and international level is good for me. Even training with the players at Celtic has made me better. Doing that with Scotland as well will help me improve even more.''
He knows, too, that he can improve. ''I'd like to score more goals. With Celtic, you get a lot of chances in games and I should maybe score more,'' he said of a record that show 11 goals in 51 appearances.
Forrest has also shown versatility by switching inside to play just behind a central striker. His pace can cause severe problems to a centre-back and he has the ability to pick out a pass. He is relaxed about playing anywhere across the front for Celtic and has now become accustomed to being asked both to play and to break down defences.
Sitting in the Scotland hotel near Erskine, he is pleased to be in the company of several Barclays Premier League players. ''You look around at meal times and there are attacking players all around you,'' he said. ''Loads of them are playing at a high level in England. That's got to be good for Scotland.''