Messi can play well till his fourties if he want but I am not sure he will play well in Premier League after his 35s.
I doubt if he will play till forties. 38 may be the last age for him to play in a football match. But it is purely our speculation, we don't know what he already plans for his career in the old age. But I disagree to underestimate him to play in Premier League. Never judge that he won't play well till he tries to play there for one season at least.
I have seen it before happening in English and Italian leagues, with players at 40 playing very well. Obviously they are not fast but these players never tend to be about speed in the first place so Messi should do well for many more years, obviously injuries might set in later but he is a well managed player with good diet and exercise, he will be fine:)
Messi is no longer as fast as he used to be and he also helps his team's defence much less than other players in the team.
It's far from the demands of modern football and can only work if the whole team is subseauted to that one player.
However, it has been shown in recent years that such a system no longer works and that Barcelona doesn't win trophies like it once did, especially the Champions League.
Messi is still fast that he hasn't the endurance to make a lot of sprints.
He can still make the difference in this team due to his amazing technique.
The reason why Barca do not win a lot of title isn't Messi but the problem is in other positions.