Fresh manure should be composted first - not sure what you mean by "aged manure." When preparing a bed, I put 1/3 composted material back in to till. But I have been amending the soil for multiple years. Much depends on the quality of your soil, as you may need other amendments such as sand if it is heavy clay. Organic material means more than just manure.

If the manure is well aged you can dig in as much as you want, your veggies will love it !

How "aged" is aged? Cow manure needs to mellow for quite awhile or it will burn your plants. Another issue is weeds -- manure is often loaded with weed seeds. OTOH, it can be great compost. If you're confident the manure is well-aged, I suggest you use it sparingly this planting season and mix it in very well. See how you do with weed germination and if all goes well add more in the fall. Happy gardening.

Thanks for the advice! The manure is about one year old; has been sitting outside for that long.