what is not for long?
Trez is not an an energetic player. He is does not have pace . He only knows how to finish. You don't lose that ability with age, and since he lacks pace and energy, we don't have to w orry about that either. A 34 year old Trez won't be that much different than this current one. So Huntelaar would have to wait say 3 years before he becomes a regular. So he would be around 28, 29. Yeah, Let's see how willing he is to wait that long and risk his World cup and Euro chances.
About your second point. What are you trying to prove? We don't know how much the offer is for sure, and we don't know if any players at all will be part of the trade so anything you say about the deal is hypothetical. And age is nor a problem here. 28 years old? So he has at least 4 years of top football in him. 4 years could mean 2 titles and a CL. Why not then? Especially considering that he has attributes of all our strikers in him.
and all this hype about Huntelaar is annoying. The easiest market to find players in is strikers. There has never been a shortage of good strikers in recent history. And alot of them go for cheap before they become big Losing out on Huntelaar is not big deal since there will always be other good ones that will pop up. On the other hand, the number of good CBs and fullbacks is very rare. Hence why I would rather not splash heavy money on a sub striker when there are rare gems like Zapata waiting around