Its almost like he peaked two years ago then ?
I don't think it's a question of him peaking when he was 26, if that's the point you're making.
That's true of strikers and wingers certainly (that they peak between ages the of 23-28), but I think floaty AMs tend to have their peaks in the 26-31 age bracket. Look at Pires, Zidane, Kaka, Iniesta - all produced at a high clip till they were 30-31. Silva is 30 and still playing well. I reckon he has another year left enough him as well. Same with Cazorla, who's actually re-invented himself as a CM.
The issue with Lallana is more of talent than of him being past his physical peak, I think. When he signed, there were people who were calling him the English Silva, which was laughable. I said in that thread that he was closer in talent to the likes of Osman and Pedersen rather than Silva, and I was roundly laughed off. His career numbers now seem very much in that bracket.
It isn't about his ability on the ball or his work rate, I don't find him an intelligent enough player. His knowledge of when to pass, and when to run beyond the defence is quite ordinary. That's the difference between him and top AMs. Technically, he can match them, but that's no use if he doesn't have high game intelligence.
Take Kuyt for example. Someone in some thread said Lallana was like Kuyt with better technical ability, which I thought was deeply insulting to our Dirk. Lallana is clearly streets ahead of Kuyt technically, but Kuyt's game intelligence was far far superior. Kuyt's off the ball running was absolutely superb, and while he was quite poor on the ball, he knew how to create space for teammates, how to defer them when necessary, and most importantly he knew how to make simple finishes (even under pressure).