I think part of the problem is that there are a lot of question marks over the younger players in the squad, as much as it is an issue with older players
Goalkeepers
1. Alisson
13. Adrian
62. Caoimhin Kelleher
Defenders
2. Joe Gomez
4. Virgil van Dijk
5. Ibrahima Konate
21. Kostas Tsimikas
22. Calvin Ramsay
26. Andy Robertson
32. Joel Matip
46. Rhys Williams
47. Nat Phillips
66. Trent Alexander-Arnold
Midfielders
3. Fabinho
6. Thiago
7. James Milner
8. Naby Keita
14. Jordan Henderson
15. Alex Oxlade-Chamberlain
17. Curtis Jones
19. Harvey Elliott
28. Fabio Carvalho
29. Arthur
43. Stefan Bajcetic
Forwards
9. Roberto Firmino
11. Mohamed Salah
18. Cody Gakpo
20. Diogo Jota
23. Luis Diaz
27. Darwin Nunez
As you can see, there are 12 players who are 29 or over. They make up the core of the side, but only because those pushing them from behind are not really dislodging them. Only Jota, Diaz and Konate would be considered first choice, the rest only playing when they are being rested, or they are injured. So, not only have those aging players to be replaced, but they have to be replaced by first team players.