why is the youngest sibling never taken seriously ?

as a cadet myself, i often found my opinion and remarks ignored or when im lucky, mocked. and when i say 'lucky', i only talk about the part where they actually 'cared enough' to listen. whenever theres a fight or a dilemma, they will ask anyone (even my niece who isnt the youngest sibling) for an answer, advice, or even worse, unsolicited advice that will be taken seriously. not to brag, but i speak more languages than all of them, i was often called smarted or maticulated but still ! never taken seriously and the only excuse is that im 'too young' or 'its old people stuff'... im 20.

i never thought about it before i turned 19, because i always thought that it was normal and its 'not that deep' until i noticed my other friends that were younger (17, 18 and cousins that are 16) who's opinion actually mattered in their family.

im over sensitive, but so is my older sister and yet my mom is always on the phone with her complaining about family drama or even asking her to go shopping, my mom never did that with me, if she wanted to take me shopping she would bring my other sister with us so they could walk and talk while im behind not even allowed to listen.

next thing is when they stop talking when im around, i get some stuff might be personal, but when theres 10 people in the room and u suddenly stop when i get there because its ' adult stuff' how do i take it exactly?

the closest sister i have to my age is 14 years older than me, so for 14 years she was the youngest, yet her opinion is the one that matters the most, she could say anything and everyone would go silent just to listen to her, meanwhile when i speak, they change subject WHILE im talking :D

the next thing is the feeling of being ignored, when stuff are being organized, im the last to know about it, when they're all hanging out together, they usually make me stay with their kids so i can take care of them (too young to listen to family drama, but old enough to change their kids diapers XD), or when we need to take the cars and we're like 10 people, im always sent to the boring one because they all 'friends'.

being the youngest is being excluded from everything because you werent there for most things, especially when the older sibling could actually be your parent because of the age difference, and i genuinly cant do it anymore. my dad went to the hospital because of an infarctus and i had to stay with the kids because my oldest siblings wanted to stay with him, as if i wasnt worth seeing my father, and the reason he had one was our family (his siblings) that led him to it, and when i dare sharing my opinion, they look at me and turn their head to continue their conversations. i dont know how to change it anymore and talking about it with them never fixes anything, theres always deeper problems, oh and talking about deeper problems, when i do have problems that in my opinion are deep enough to make me depressed for a good two weeks, they will always invalidate it and make it seem like im doing too much. communication is impossible, im waiting to get out of here as soon as i can.