Trivial question about puberty and the Tanner stages

[John_Doe]

Most of the sources that I've come across claim that menarche is considered delayed if it hasn't occurred by age 15 (and whatever equivalent milestone there is for boys, the rule seems to be that the average age for that milestone will be one year later than the female average), around 98% of girls have started menstruating by 15 (or at least girls in developed countries where malnutrition is less likely to be an issue. The body won't prepare for pregnancy if it doesn't have enough fat to sustain one so if girls over 15 haven't had their first period for that reason I don't think that's age-related per se). Some sources claim 16 but 15 seems more plausible to me because menarche is not 'supposed' to take more than 2 years after thelarche to occur and virtually every source I've come across claims that thelarche is delayed if it hasn't occurred by 13 (the exceptions being one AI-generated answer that claimed it's delayed if it hasn't occurred by 12 and a site claiming that the average age for puberty is 13 for girls and 14 for boys which is demonstrably false, it's well-documented that the average age for thelarche is 10 and for menarche it's 12 or at least that's the general or traditional estimate, in the developed world some stats go lower, at least for certain demographics, but I haven't seen anything higher). Some sources will claim menarche is delayed if it hasn't occurred by 15 or within three years after thelarche.

Is or should Tanner stage 5 be considered delayed if it hasn't occurred by 15 (for girls, 16 for boys)? I know that Tanner stages 2-4 (since 1 and 5 are just pre-puberty and the completion of puberty respectively) don't necessarily take a neat one-year to complete but typically menarche occurs in stage 4, yet I've come across sources that claim Tanner stage 5 is delayed if it hasn't occurred by 15 (in girls). Should it be/is it generally considered to be delayed at 16 for girls and 17 for boys?

Are the Tanner stages arbitrary to begin with? It's interesting to note that, apparently, in Tanner's original research some girls who had reached stage 5 reverted back to stage 4 (or perhaps certain characteristics) and many people never reach stage 5 to begin with.

[Scorchingwilde]

The tanner stages are rough categories to describe processes of physiological changes related to endocrine factors/hormones, and the rate of change can be different between individuals or for different tissue types or areas of the body. Hip changes happen even as late as 15-16 even if menstruation happens and becomes stable earlier, for example, and in addition to growth spurts in height in adolescence, anyone who isn't exposed to a lot of estrogen that fuses growth plates (usually boys/men) is likely to have another in what is considered full adulthood in the west, from around 18-24 or 'college age.' It's complex

[DANAT4T]

Most of the sources that I've come across claim that menarche is considered delayed if it hasn't occurred by age 15 (and whatever equivalent milestone there is for boys, the rule seems to be that the average age for that milestone will be one year later than the female average), around 98% of girls have started menstruating by 15 (or at least girls in developed countries where malnutrition is less likely to be an issue. The body won't prepare for pregnancy if it doesn't have enough fat to sustain one so if girls over 15 haven't had their first period for that reason I don't think that's age-related per se). Some sources claim 16 but 15 seems more plausible to me because menarche is not 'supposed' to take more than 2 years after thelarche to occur and virtually every source I've come across claims that thelarche is delayed if it hasn't occurred by 13 (the exceptions being one AI-generated answer that claimed it's delayed if it hasn't occurred by 12 and a site claiming that the average age for puberty is 13 for girls and 14 for boys which is demonstrably false, it's well-documented that the average age for thelarche is 10 and for menarche it's 12 or at least that's the general or traditional estimate, in the developed world some stats go lower, at least for certain demographics, but I haven't seen anything higher). Some sources will claim menarche is delayed if it hasn't occurred by 15 or within three years after thelarche.

Is or should Tanner stage 5 be considered delayed if it hasn't occurred by 15 (for girls, 16 for boys)? I know that Tanner stages 2-4 (since 1 and 5 are just pre-puberty and the completion of puberty respectively) don't necessarily take a neat one-year to complete but typically menarche occurs in stage 4, yet I've come across sources that claim Tanner stage 5 is delayed if it hasn't occurred by 15 (in girls). Should it be/is it generally considered to be delayed at 16 for girls and 17 for boys?

Are the Tanner stages arbitrary to begin with? It's interesting to note that, apparently, in Tanner's original research some girls who had reached stage 5 reverted back to stage 4 (or perhaps certain characteristics) and many people never reach stage 5 to begin with.

I honestly wouldn't worry about it too much. I am also jealous of the female reproductive system.

[John_Doe]

The tanner stages are rough categories to describe processes of physiological changes related to endocrine factors/hormones, and the rate of change can be different between individuals or for different tissue types or areas of the body.

I know but I'm curious about what's standard or at what age Tanner stage 5 is considered delayed. I know that some girls don't get their periods until 17 and the youngest known mother was only 5 when she gave birth (browsing some reddit threads a while ago I found some rare 17s and maybe only one solid 7; one other person said she had 'spotting' at 7 though and some others said '7 or 8.' Even that definitive one said she only had a couple of periods at 7 and they didn't stabilize until 8. I found a few 8s which surprised me) but that's atypical, at least when malnutrition or certain medical conditions aren't an issue.

Hip changes happen even as late as 15-16 even if menstruation happens and becomes stable earlier, for example,

I've read that female hips begin to widen at the start of puberty but different sites claim this continues until 18-20; becoming slightly more narrow after 25, 25-30; narrowing after 40, or even that they continue to widen well into one's 70s for both men and women.

and in addition to growth spurts in height in adolescence, anyone who isn't exposed to a lot of estrogen that fuses growth plates (usually boys/men) is likely to have another in what is considered full adulthood in the west, from around 18-24 or 'college age.' It's complex

I am not well-read on this but my understanding is that most girls stop growing by 15 or 16 (because of estrogen fusing growth plates) and that growth after 16, in girls, is rare unless one started menstruating late and that most boys finish growing between 16 and 18 even though growth into one's early 20s sometimes occurs. Reasonably or not, we consider 18 to be the start of adulthood even though some people continue growing or developing in some way after 18 or never develop in certain ways or to an expected degree so I'm interested in what's standard (also, I don't know how much growth has to do with sexual maturation per se, even though testosterone/estrogen is obviously a factor).