Hello carey189,
Thanks for reaching out to Apple Support Communities. Upon review of your post, it seems that you are having an issue downloading older photos on your iPhone. We can see why you’d want this taken care of, so let us help from here! Let’s start by reviewing the following article which may help: Get help with iCloud Photos. This article explains: “If you have Optimize Storage turned on, you might not have all of your original photos and videos on your device.” This may be why you are seeing your older photos requiring download to be visible on your iPhone. This feature can be disabled, if you wish.
Regarding why you cannot download the photos when you tap on one, that could be due to full iPhone storage (How to check the storage on your iPhone, iPad, and iPod touch) or network issues.
Please let us know if you have follow up questions, so we can continue assisting. Take care!