So to finally answer your question, the second gear still negatively affects luffy and chips away at his lifespan, but when compared to the time he first developed the technique, the effects are not that great.
Of Roger pirates have told that the techinques of luffy such as GEAR 2ND and GEAR 3RD puts too much strain on his body and by using those techniques he is slowly decreasing his life span and when luffy told the dark king that he has another technique Gear 4th ,the dark king told by doing so he is putting more strain to ...
Akin to Gear 2, using Gear 4 causes Luffy's metabolism to increase rapidly. In fact, after Luffy stuffed himself to a bloated size in his fight with Charlotte Cracker, using Gear 4 once made him burn off the massive amount he had eaten in a manner of minutes.
After the two-year time-skip, Luffy's control over Gear Third has improved vastly and made him stronger as a result. While using it before the time-skip inflated his entire arm, Luffy is seen being able to control the amount of air and the location at which it gets stored at will.
Luffy's rubber body is his actual power and can be considered Gear 1. His powers result in allowing him to stretch and bend his body in a number of ways. This talent is known as the Gear 2. It is a method that allows him to enhance blood flow to his muscles, allowing him to move faster and with more strength.
The more he laughed, the better he seemed to fight. Throughout the clash against Kaido, fans could see him laughing even though he was fighting a high-intensity battle, which just goes to show how important it is to his character.
Using Second Gear has definitely shortened Luffy's lifespan. The technique involved him pumping blood through his body at an accelerated rate in order to give himself a boost in speed and power.
Gear Five gives Luffy the ability to fight freely and without much constraint as shown in his bout with Kaido and now Rob Lucci. This means Luffy can be hit with deadly attacks that now leads to his physical appearance forming either a shape of the weapon, or showcases the manner in which he was hit.
While using Gear 5th, Luffy is able to extend his elasticity to inanimate objects. Luffy's devil fruit awakening allowed him to beat Kaido, who was considered the "Strongest Creature in the World." In his Gear 5th form, there are not many One Piece characters who can defeat him.
Yes! Of course, Luffy's Gear 5 is the peak of his colossal powers. He can literally do ANYTHING with his devil fruit powers right now, as he transforms into the Sun God Nika when using Gear 5, making his devil fruit the strongest in existence so far.
Gear 5 makes Luffy much tougher and stronger, however, its biggest asset is that it makes him fight with even more creativity and freedom.
2 Gear Fourth: Snakeman
All of Luffy's attacks in Snakeman are ranged and hit the target in an unpredictable fashion. The weak point of this form is that it sacrifices the extra defense that Gear Fourth offers for additional speed.
With his devil-fruit powers, Luffy is able to manipulate his rubbery body into various forms, which he calls “Gears.” Currently, Luffy has managed to unlock up to five gear forms, and his fifth gear is known to be his peak form. He was able to unlock Gear 5 after awakening his devil fruit.
While the effects of this technique have been mitigated in post-time-skip One Piece thanks to training, the prior uses have already caused irreversible damage to his body. Luffy dies from gear 5th strain on his heart and law gives up his life so they can win. This causes Luffy to go into gears without dying.
So to finally answer your question, the second gear still negatively affects luffy and chips away at his lifespan, but when compared to the time he first developed the technique, the effects are not that great.
Gear Second established itself as Luffy's go-to form over time, and it is extensively used by the Straw Hat captain even now in the series. With incredible speed combined with ferocious power, Gear Second has helped Luffy conquer some tough enemies by making him several times stronger.
Fan theory suggests that Luffy will awaken Gear 6 in One Piece. The concept of Gears was introduced in the Enies Lobby arc of One Piece when Luffy brought out Gear 2 against the CP9 agent Blueno. His skin turned pinkish and heated up, allowing our main character to move faster.
I don't think you can simply say "he can beat an admiral" because even within the Admirals, there's such a huge difference in power. I personally think that Luffy could probably just barely beat Aokoji now (or in the near future), and he could fight but not beat Kizaru, and has no chance of beating Akainu.
Luffy's gears also put pressure on his body. Since using them is obviously more dangerous than smoking or drinking, Using gears repeatedly will eventually shorten his life to say 30 or 40. His 2 year training probably made him resistant to immediate side effects like weakness and becoming a dwarf after gear 3rd.
In addition, Luffy still has his standard weakness to cutting attacks.
Weaknesses. Despite these advantages Luffy is not immortal. Though immune to lightning, he can be damaged by other elements such as fire or ice, attacks involving cutting or stabbing and Haki-infused attacks.
Luffy's greatest power-up to date is, undoubtedly, Conqueror's Haki coating. During his fight against Kaido, Luffy observed Kaido coating his weapon in Conqueror's Haki. After this realization hit him, he was able to use a crude version of this technique himself and could coat his fists in Conqueror's Haki.
Short answer, no. As far as canon story is concerned, Luffy won't marry Boa Hancock.
Luffy did not eat the “god-god fruit.” It's the hito hito (human human) fruit model: sun god nika. Meaning it's based off the sun god, not that it makes you a god, so unless he can somehow “stretch” his lifespan, no he is not immortal.