A person cannot become Autistic, people are born Autistic.
Not talking is not necessarily a sign of Autism either, many autistic people are non-verbal but not all and there are other reasons for people not talking.
A person is born autistic - they do not become autistic.
A person doesn't become autistic and being quiet doesn't make someone autistic - a person is born autistic.
A person is born autistic - no one knows the cause of autism.
A person cannot become Autistic, a person is born Autistic. Not speaking does not mean that a person has become Autistic, there are many reasons why a neurotypical person may stop speaking.
A person doesn't 'end up' autistic, a person is born autistic. Not all autistic people are non-verbal either.
Yes, autistic people can live as long as neurotypical people or people with other neurologies. There is nothing about autism that would shorten a persons lifespan.
Yes, autistic people can have pets and often prefer animals to people. As long as a person is able to care for a pet, whether autistic or not, then they can get a pet - some autistic people also have pets as support animals for comfort and company.
Autistic people (identity-first language) live as long as Neurotypical people, Autism doesn't impact on health in such a way that could shorten someone's life. In theory Autistic people have a slightly shorter lifespan because some Autistic people have problems identifying harmful behaviour - such as children who wander near water - also due to prejudice Autistic people may be more likely to be unemployed or be denied equal medical care which impacts on life.
Yes, of course autistic adults can get married. There are no restrictions on autistic people getting married, as long as they can consent to being married there's no reason for them not to.
Yes, Autism has a big impact on a persons social life. People who are Autistic have social and communication problems which means that making and maintaining friendships is very difficult, and often neurotypical people can dislike Autistic people because they don't mimic neurotypical body language or because Autistic people act differently to neurotypical people. Autistic people also often struggle to maintain social interaction, it requires a lot of extra effort for Autistic people to be around other people so they may not be able to cope with being around people for too long, especially in large groups or in busy places. Autistic people can also commonly be unemployed, in the UK around 85% of Autistic adults are not in full-time employment or education, this limits Autistic people's ability to meet new people, maintain learned social skills, and means that Autistic people don't have the money to socialize. Autistic people are often very social and want to have friendships, but their problems and their situation can mean that they end-up becoming very isolated.
There's no such thing as a mild form of Autism - a person is either Autistic or they're not, how they're effected can be mildly but this can change throughout their lives. There are no restrictions on Autistic people owning a gun, as long as they have the capacity for responsible gun ownership.
You are born with autism and have it all your life. However, with skills training and preparation, the effects of autism can be better controlled so that it seems to be less obvious when one is older.