He'll be 27 by the summer and rightly or wrongly, the money men at clubs will take that into account his resale value and how many years he's got left in him.
For example if you say a player is past his best at 32 (you could use any age, it makes no difference), a 27 year old costing £30m would cost you £6m per year, where as a 22 year old costing £30m would cost £3m per year. Then of course a 22 year old could potentially be sold for a similar figure in 2-3 years time where as the 27 year old's value would be halved after a couple of years.