Who are the many others? Fed, Nadal and Agassi alone have won Slams >33 in the 21st century. No other current professional has reached a Slam semi older than 32.
My comment was about sticking around at a high level not about reaching slam semis. There's many who keep on playing well into their 30-ties and still are ranked pretty high:
1) Monfils (33 yo, rank: 10)
2) Fognini (32 yo, rank: 12)
3) Wawrinka (34 yo, rank: 16)
4) Isner (34 yo, rank: 19)
5) Tsonga (34 yo, rank: 29 and growing)
6) Cuevas (33 yo, rank: 45)
7) Verdasco (36 yo, rank: 49)
8) Simon (34 yo, rank: 55)
9) Gasquet (33 yo, rank: 61)
10) Andujar (33 yo, rank: 64)
11) Seppi (35 yo, rank: 75)
12) Kohlschreiber (36 yo, rank: 79)
13 Anderson (33 yo, rank: 91)
14) Karlovic (40 yo, rank 95)
This is just TOP100. They are all gatekeepers too. Many more in 100-200.