Some catchers mentioned upthread and what they did before and after their age 33 seasons:
Chooch - Age 31-33: 367 G, 10.3 oWAR, 5.3 dWAR, 127 OPS+
Age 34-35: 202 G, 3.9 oWAR, 2.1 dWAR, 97 OPS+
Age 36-38: 201 G, 1.5 oWAR, 1.4 dWAR, 76 OPS+
Boone - Age 31-33: 336 G, 2.4 oWAR, 2.3 dWAR, 86 OPS+
Age 34-36: 424 G, 1.0 oWAR, 6.4 dWAR, 66 OPS+
Age 37-42: 715 G, 4.7 oWAR, 10.0 dWAR, 79 OPS+
Yadi - Age 31-33: 393 G, 5.6 oWAR, 4.8 dWAR, 98 OPS+
Age 34-36: 372 G, 5.1 oWAR, 1.8 dWAR, 95 OPS+
Age 37-49: 241 G, 1.6 oWAR, 1.1 dWAR, 74 OPS+
JT - Age 31-33: 373 G, 11.3 oWAR, 4.6 dWAR, 115 OPS+
Everybody dropped off somewhat after their age 33 season, not surprisingly. Chooch was the only one of this group close to JT offensively age 31-33, but he dropped off defensively and even more offensively afterwards. Boone was never much of an offensive threat but still dropped off a lot though became much better defensively based on dWAR, to the point where he is in the top 20 among catchers in career dWAR . I can't imagine there are many if any others who had such a defensive upturn at that age. Yadi maintained his offense through age 36 (though he was not at JT's level), but his defense dropped off noticeably.
It goes to show everyone is different, but it still seems the odds are long for JT's performance not to drop off a lot in the next few years.