Need help! Read below.

I (27 M) asked her out( 43) and she turned me down.

I asked my former manager out on a date and she said it was inappropriate of me to ask her. I left that position 5 months ago when i used to work with her. We have met few times for lunch and hung out but nothing happened. I gave her birthday present and few small things like flowers and stuff and wrote her a letter on my last day at work about how thankful i am and all. She would ignore my texts and says she is always busy but when we meet it’s always fun. I asked her over the phone and she said we worked together and we are friends and it’s the age difference. That was a week ago. Should I text her again or anything i can do make her change her mind? I thought she gave me signs as she spent all day with me. What should i do? I really like her as a person but i feel like I cannot be friends.