I don't think I said anything about him playing after his current contract, but barring another catastrophic injury - and he's had two already - 35 is not 'aging out' of the QB position in 2025, much less 2029. Yes, we'll need to start looking to the future at every position eventually. When that will be with Dak is hard for anyone to say. He could have two miserable years in a row during his current contract and the future is then now, or we could somehow go to 2 NFCCGs or SBs in the last 2 years of his contract, which would get him yet another contract.
The idea of predicting the future is folly. For goodness' sake, Flacco is still starting. What is he, 40? Brady, Rodgers (I know, he's in freefall, but there are MANY posters here who think we should have gone after Rodgers post-35), Stafford is 37, Brees was 42 when he stepped away, Cousins is 36 and doing exactly the same thing that he's always done. Rules changes and players taking care of their bodies has increased their shelf life. If Dak can win, I don't care how old he is. Dak led us to 12 win seasons 3 years in a row before he got hurt this last time. Talk about post-season success all you like, but you have to get to the post-season first. 12 win years are very good in the NFL, 13+ wins are outstanding, and not many teams get 13 in any given year.