Tika is given by elders to their younger relatives. With Dakshina, it's generally the opposite, but the exceptions apply. Women and girls receive Dakshina from their parents and elder siblings. Even men get it from their in-laws, maternal grandparents and maternal uncles and aunts.

How much do you typically get? Ranges from Rs 50 to Rs 2000 for me personally now that I am an adult. I used to get in the range of Rs 5 to 100 when I was a child (not adjusted for inflation, of course).

Do people of all ages receive... Yes, but your age is closely related to the complicated dakhshina-heirarchy. As you get older, there will be more people who give dakshina to you, and there may be more you have to give to because of your daughters' (or nieces') birth, their marriage and their children's birth.

Historically, what is the idea ... Not an expert, but my guess is that the ritual of giving dakhshina in exchange for tika was perpetuated (or, perhaps, even initiated) by priests who benefited from this system. Or I could be being needlessly cynical here. Please correct me if you think I am wrong.

Did people use to give something other than money... Oh yes. Its common to give clothes or metalware and a little money (like a Rupee). Dhaka topi and dhaka shawls are quite common in my neck of the woods, especially for older people who wear traditional clothes.