is it possible to learn a needle at age 20?

Yes you can, but the stunts you list require different skills, not just flexibility.

You will probably make better progress if you start to include some Martial Art stretches in your routine, or even learn a 'standard' martial art such as Shotokan karate or Tae Kwon Do.

The scorpion, needle, and bow-and-arrow are all variations of the same basic move. The needle is the easiest to achieve, but your preparation is through 'box splits' rather than by improving your front split capability.

The Scorpion is just a Needle with added twist in your waist, so that both arms can reach behind your head to hold the foot. Your knee bends, and this variation means that you need more 'quad stretch' range-of-motion in the front of your thigh.

The most difficult is the bow-and-arrow, because you need to develop your box splits to allow 180 degrees of separation, AND you need to be able to lean sideways in the same stretch, so that your elbow (and ideally the same shoulder)can rest on the floor in front of one thigh, while the opposite hand reaches over your head to grab the foot.

For this stunt, and for the leaping splits you listed, Karate stretches are ideal. In Karate, a 'double front kick' is the ultimate form of box split, but performed so quickly that both feet can deliver blows as the move is completed. As well as flexibility, this requires a very fast & free 'release' in the stretching muscles.

These muscles include your Hamstrings and your Adductors. Slowly moving into a stretch such as the Front Split is a different type of challenge from 'flying' into a similarly extreme stretch to deliver a Split Kick to attackers on both sides simultaneously.

To improve your box split (needle within a week, if you can already oversplit in Front Split position), you should sit with your legs as far apart as possible, and lean forward with your back as arched as possible, as if you are trying to rub your bellybutton on the floor. If you can already rest your elbows on the ground between your knees, you will make rapid progress. Read or watch TV in this position, occasionally deepening the stretch by 'twerking' your hips.

Alternately twerking and crunching (curling and arching) can help to produce faster progress, but you should try to develop this position as GENTLY as possible; too much progress in one session can cause a reaction that tenses up the muscles and REDUCES your ability to get into the position next time you stretch.

While you are progressing the width of your box split position, you can also develop the waist movement available during the stretch. Ballet dancers habitually practice arm positions (this helps you to keep your neck long & free while stretching your hips out) in a wide seated position; this habit will eventually help you to get into the bow-and-arrow.

You could make this happen, but there is something you have to take in consideration, as my coach says, you either have mobility or you don't, the most important thing is for how long are you doing this stretches that take about 40 min? If you have just started doing them, than you should be doing this in a couple of months. If you do this for 3 months and you don't see improvements than you should reconsider. I hope this helps and take in consideration that this is just an opinion.

yes !!!!!!