As a goalie that also recently started at age 30 perhaps I can offer a few tips.

First... the endurance and strength will come with time. Don't worry about it in a game, adrennilin will give you what you need when you need it. In practice you are more relaxed so you feel it more.

When you start getting tired.. take a break for a few. Forwards don't understand why you are so tired. It is an easy skate for them, you are jumping up and down in 65 lbs of pads, and facing more shots, faster than in any game, anywhere.

If I am in a practice session, and start to get tired, I stop going down. I spend most of my time working on angles, staying up, using my stick.. etc until my strength comes back. Remember, these drills are for YOU not for the shooters (as they mistakenly think)

You have to use them to your advantage. If you get tired, and start getting beat easily, it can errode your confidence. Make the drills work for you