Excellent points.
While Varitek did have his first season over .800 at age 27, it took him until ages 31-33 to do it 3 years in a row.
I don't believe, his defense was not all that highly regarded, at first, but maybe catching Wake early in his career hurt his numbers. He had 57 PBs from 1998-2000, including 2 seasons leading the league, there. He also allowed 58 WPs in those 3 years for a whopping 115 PB+WP. His CS% was never great (23%,) but to me the most telling improvement came in the CERA area.
I normally frown upon just using overall CERA by catching tandems, since most of the time, they tend to catch different SP'ers almost exclusively, but I will list the year by year CERA numbers to show VTek's improvement occured mostly in his early 30's:
1998: 4.10 Hatteberg/ 4.29 VTek (age 26)
1999: 3.13 Hatteberg/ 3.98 VTek (age 27)
2000: 3.96 VTek (age 28)/ 5.02 Hatteberg
2001: 3.00 VTek (age 29)/ 4.60 Hatteberg/ 4.75 Mirabelli (generally regarded as + on D)
2002: 3.74 VTek/ 3.83 Mirabelli- essentially tied
2003: 4.46 Mirabelli/ 4.49 VTek- essentially tied
2004: 4.18 VTek/4.26 Mirabelli- same
2005: Ooops! 3.73 Mirabelli/ 5.02 VTek (Mirabelli, basically caught only Wake)
2006: 4.54 Mirabelli/ 4.84 VTek/ 5.58 JLopez/ 5.26 J Bard
2007: 3.80 VTek (age 35)/ 4.09 Mirabelli/ 3.95 K Cash
2008: 3.66 VTek (age 36)/ 4.81 KCash
2009: 3.87 VTek (age 37)/ 5.22 VMart/ 5.36 Kottaras
2010: 4.05 VTek/ 4.28 VMart (VTek was no longer the starting catcher at age 38)