The simple answer to the question is that it will be difficult to duplicate. Wakefield started pitching consistently for the Boston Red Sox at age 28 in 1998. Dickey was 35 when he pitched his first season with the Mets in 2010. But the legend continues with knuckleball pitchers, as the lack of strain on their arm allows them to pitch longer than conventional pitchers. Pitchers such as Phil Niekro and Charlie Hough were able to pitch well into their late forties. Though Wakefield has struggled over the past two seasons, he still has a little in the tank.
Wakefield also benefited from pitching for a Red Sox team that allowed him to struggle and kept him around. Five times, in his 17 year career with Boston, he pitched to an ERA that was over 5.00, including 2010 and 2011. From 1999-2002, he spent half the season in the bullpen and half in the starting rotation. Perhaps Dickey can make the transition if necessary.
Now, if you want some pros in this argument, you can point to Dickey's last two seasons. His WHIP has been extremely low for a knuckleball pitcher and his overall numbers have been more consistent. It is only a two year sample, but it is nice to know that his 2010 season is not a fluke. Dickey has a team option for the 2013 season that should be exercised as long as he maintains his consistency.
Wakefield is going to be 45 whether he pitches in 2012 or not. Even if Dickey pitches until he is 45, that will only be 8 more years. But its still a long time from now. Added to his partial seasons before he joined the Mets, he would have 17 MLB seasons, a very respectable career. He all know RA is in tremendous shape, and that will factor in his longevity. And assuming his arm holds up, which it should, he will be able to pitch well into his 40s. 20 years is a little too much to ask for, but there is no doubt that RA Dickey and his knuckleball will be around for a while.