There should not be any quotas for people based on age for any of the party candidate lists. People have all ages have managed to gain political office over the course of the hundreds of years that elections have happened in the West, and quotas would not be really helpful.
No, there shouldn't be a youth quota at all. Whether or not you want to be part of a party is up to the individual, and there shouldn't be mandates. As soon as you start forcing people to choose, they become resentful and disgruntled. It is never a good idea.
No, there should not be quotas for youth in party candidate lists, because the youth are the future of the party. The youth should be allowed to rise and fall on their merits, like any other politicians. Often, the young people will do an even better job, because they have longer to live in the consequences of their own actions. We should accept their youth and welcome them into politics.
Quotas prevent a fair playing field. Anything that requires a quota will allow a weaker person to be part of a group even though they don't deserve it. Quotas do not work in hiring or in party candidate lists. Quotas should be abolished altogether. They do nothing but denigrate the lives of deserving people.
There should be no limits to the requirements for political candidates. If there is a quota for young people, it would skew the natural order of things. Often, politicians are older because they have more experience. It should not be necessary for young people to participate if they do not want to.