This thread is crazy!
I'm female but if I was cast aside every time I didn't climax, my sex life would probably be only 25% of what is has been!
There has only been one of two partners where the sex has been the best at the start. Usually, it has improved over time for both sides, as nerves disappear, attraction grows, there's a greater understanding of what works and what doesn't, you get closer and turn each other on more etc.
There are a number of reasons he may have issues. The chances of it being his age isn't the most likely. It may be all or any of the following: nerves, lifestyle, drink, cocaine, porn, too much self service - there is a big difference between the feel of a hand & a vagina and it takes time to get used to it.
My own experience is talk about it fine but don't overly focus on it. Enjoy how things are for now and unless it's a big issue it will rectify itself in few weeks. If it doesn't, then it's a larger problem than simply out of practice or adjusting to a new relationship.
The only word of caution is the too tired piece.....that to me indicates selfish lover. If he's trying but failing that's different but if he's just lying there and it's all on you, I wouldn't stick around too long.
Men who are selfish is bed tend to be selfish everywhere. Unfortunately, a man who isn't selfish in bed, doesn't guarantee anything either but it helps.