I've found that I prefer being called autistic over any other alternatives and that's how I describe myself as well.
I think it's because my autism is part of who I am and describing me as a 'person with autism' makes it sound like this is some negative thing that I've been afflicted with. Of course, there are struggles and difficulties I face because of my autism, but that doesn't mean that my being autistic overall is some negative thing that I hate and wish I didn't have. It's no different than how I view my gender identity and sexuality, there are difficulties I face because of me being transgender and lesbian but that doesn't mean I think me being trans and lesbian are negative things.
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"For God so loved the world that he gave his only Son, so that everyone who believes in him may not perish but may have eternal life." - John 3:16 (NRSVUE)
Remember that it is never too late to accept God's love into your heart and to believe the truth that Jesus Christ died for your sins, was buried, and rose from the dead after three days. Christ's sacrifice was unconditional and it is never too late to invite Him into your heart as your personal Savior!