The 29-year-old Wigan defender is one of the most experienced players in Craig Levein's squad for the friendly against Denmark at Hampden on Wednesday night.
The game will serve as a warm-up for the Euro 2012 qualifying double-header against Czech Republic and Lithuania next month with Caldwell admitting that the Scots' hopes of making it to Poland and Ukraine next summer are "in the balance".
Scotland have not qualified for the finals of a major tournament since the 1998 World Cup in France and for the qualification campaign for Brazil in 2014, Levein's side were handed another tough draw in a group including Croatia, Serbia, Belgium, Wales and Macedonia.
Speaking at the Scots' camp on the outskirts of Glasgow, the former Celtic defender revealed his worries about missing out on the chance to take part in international football's showpiece occasions.
"I am only 29, believe it or not, but once you start nearing 30 you do start to think your opportunities are less," he said.
"Obviously the World Cup comes only every four years so this is going to be a big one for myself.
"I think it's coming at the peak of my career and it's one in which we have a real opportunity with the team we have got and the group that we have got.
"So hopefully I, personally, and the country can get there.
"You see that World Cup draw and see the challenge that awaits and
that's something to look forward to in the future, but for now we have to focus on the Euro campaign and these coming games are the most important for us just now.
"I think our Euro hopes are still in the balance.
"It's still between us, the Czechs and Lithuania (for second place play-off spot).
"Obviously having Czech Republic at home is a huge game and it will probably decide where we finish in the group.
"If we can win that one it will give us confidence going in to the remaining games.
"But we are in the position now where we have to win these two games at home and Put ourselves in a strong position for the last two fixtures."
Caldwell believes he has become a better player since moving south in January, 2010, not least because he is asked to do more defending with Wigan.
"I think the Premier League tests you every week," he said.
"The players are physical and the standard is very high so you have to raise your game and adapt to that.
"At Celtic you were more of a centre half that had to create and start play and didn't defend as much.
"At Wigan, at times you are playing Manchester United and Chelsea where you are under the cosh and you have to defend and learn how to deal with that pressure.
"Throughout your career you have different experiences and challenges and that's what brings you on as a footballer."
Wigan do not start their Barclays Premier League season until next week thus Caldwell believes Wednesday's friendly will have a two-fold benefit.
"A lot of people say it is a funny time to have an international date and some leagues haven't started yet obviously, he said.
"But I think any time you are asked to play for your country you look forward to it and you want to do as well as you can.
"A lot of players are not up to full speed but it's another game for them to get the match fitness that they need, whether it be for the start of the league or the qualifiers next month."
The former Hibernian player added: "I think the result is always important.
"You play football to win and winning games breeds confidence.
"If we get a performance that's a bonus but we want to win.
"It is going to be a difficult game, Denmark are a similar side to the Czech Republic.
"As group we are more together and more settled and the results that we have had has given us confidence and belief that we can achieve something."