Pinky action on 'fast' passages

[AX2]

I'm an adult self-learner (currently 25yo.) and I'm struggling with 4th-5th fingers fast alternate movement. For example middle C-D-C-D or E-D-E-D alternations. I know there are trill keys but I figure they're intended for trills alone, due to tone and pitch issues.

I've been doing exercises to target this, which were helpful to some extent, but I'm still too slow (350bpm)!
It's currently physically impossible for me to move them any faster. Is this a consequence of not having properly 'wired' my tendons since childhood? Is it hopeless now?

In any case, one thing I've noticed among younger players is that they often don't actually put the pinky down for these E-D-E-D-E-etc situations. Is this an acceptable workaround?

[pied_piper]

As you pointed out, children tend to be able to learn faster, but it's never too late to learn and develop faster finger movement. It just takes a bit longer as you age. It's all about muscle memory which take time to develop. Keep working those finger patterns and speed will come with time. Leaving the pinky up for C-D or E-D is used as a trill fingering and rarely as a cheat. While learning, you should avoid cheating. However, even professionals will use those occasionally when warranted. It is a judgement call, but the pinky is down for most notes because it sounds better that way. Keep practicing for speed and reserve the trill/cheat fingering for desperate moments.

[AX2]

Thanks for the reply.

Could you please listen to this at 1:53? The piccolo part.
https://www.youtube.com/watch?v=LEfZqFdXGaY
In the flute arrangement I was given, this part starts C-D-C-D (middle C). In this particular case is 'cheat' fingering ok, or is that speed still in the 'normal' range?

[pied_piper]

That piccolo part is fairly busy and with trills to boot. I think for that section, cheating with the pinky is probably OK to do.

[new2flute]

I starting playing the flute when I was 64 years old. My first lesson was given to me by my granddaughter. You're never too old.

Practice slow and with precision. The speed will come with practice.

I taught martial arts for 20 years. The phrase I used the most BY FAR was "slow down". I'm pretty sure in teaching anything involving physical activity where speed is a goal the tendency is to strive for speed over accuracy. In reality it should be the other way around. Practice slowly with precision and speed will increase naturally while the precision you've practiced will be maintained.