Sorry mate but that type of tactic only will aggravate the player.
Salary is not and should not be related to age. If you are as good as another player, who also is paid that level of compensation then it is right and fair to pay the going rate.
Regardless of the scale difference. If you work, you expect to be paid the same amount as a peer performing the same job as you. Sterling is no different.
£120K per week is not even at the top end of the salary scale in this league. The best are paid at least £200K per week, the next level down (good experienced players and young talented future stars) between £100 - £150K. That's reality.
If we do not compensate him in accordance with the norm of the league, he will go looking elsewhere. Another club will pay that amount and we lose the player.