Always put down

Question

I am always put down by my family members whenever a situation arises when there's a decision making time. Recently a cousin of mine had an affair with someone, there were many discussions which went on in the family, but no one could come to a decision. Even I though I tried helping by thinking reasonably and logically, I am put down by my members on the context that I am younger and should not interfere (despite the fact that my cousin is only 2 years older than me).

This was just an incident many times I am also cut down on the context of how I am talking(they think I am being rude,because of my tone), even though my family knows the tone in which I talk, they try to cut me down in similar situations pointing to my unacceptable way of talking. When I correct myself, by “trying” to be nice (even though I was,and was just helping them get to a conclusion), they tend to not pay heed on what I say next.

How can I get them to take my opinions more seriously?

Answer 1

The first important thing, do these decisions concern you? It sounds like it's only a discussion about other's concerns (your cousins) but you are not involved by the results? Then there is no real disadvantage for you if the result is not what you would suggest. This is important and could help you to stay cool with this situation.

Then do you really want to stay engaged in these discussions? Try another strategy. If the put you down, leave the discussion or even better the room. Don't play offended, be cool and show you have no reason to think about things if they don't want to know your opinion.
I know it is not easy and doesn't work always. But it's better than desperately trying to be accepted.

I am also cut down on the context of how I am talking

Well this is something you should change, regarding you whole future life. Your family should know you, what you mean when you say something in your way. If even they can't handle this, how should the rest of the world do?

even though my family knows the tone in which I talk

Some things don't change and must be taken as they are. But on the other hand not everything can be explained by just saying it's the way it is and it will not change. If your tone is shocking, you should adapt instead of everyone else.

Do you have an idea what they don't like in your tone? Ask them!
Start a discussion with only one family member, ask for examples, let them imitate you. Think how this ton would impact you, if heard from another person.

Now the conclusion

There is a little chance that another way of talking could also repair the "you are younger" situation!

Answer 2

Ah... I kinda could relate to this as I am the youngest in the family as well. Both my brothers are older than me by 9 and 6 years respectively. When it comes to important decision making, I will felt I am always being left out.

One good thing I think you may start first is by asking yourself "why is that so?".

Think of all these years how you have been through in the family. Have you been independent enough? Do you always ask for unreasonable requests? Consistently getting people to worry about you? Able to help your parents in settling some house matters (e.g. calling to town council and lodged complains on something happened, or it can be simple things like saving up and getting an oven for the family)?

Being the youngest in the family, your words tends to be "lighter". But, we are really lacking on the life experiences. A lot of what we think would work (logically), is often a too "ideal" solution.

So, how do you let others to take your opinions seriously? 

This question is something similar as to someone asking...

"how do I prove myself an awesome leader?" 

There are many ways, but it definitely won't be just saying out words. You will need actions to prove it.

It goes the same for this case. Hence, don't be hasten to be recognized. Observe how the adults are solving the issues. You may leave the discussion but still provide your opinions privately with one of your family members (it can be your mum or dad). It will takes time for your family members to see your maturity through those daily life, your actions, behaviors and so on as time goes by.