This depends on how hard you're working on it:
How many books have you read about social skills? How many of these have specifically been about how to make new friends?
How many times/week do you go out to do social activities like participating in local adult sports, bar trivia/bingo, or other clubs for adults?
How many times do you go up to new people to meet them? How often do you use various skills learned in the books you've read to make a good impression? How often do you ask people you like and who like you to join you at another fun event?
None of these things are actually that difficult. If you make an effort, you'll be amazed at how easy this is and annoyed at yourself for not doing the work earlier.