You don't get an abcsess from mixing water and oil based gear. That's just plain stupid. You get infection, read abscess, from pathogens in the gear, be it water or oil based. Because we are waterbased there is a higher chance of a pathogens in water based gear then in oil, the things that live in oil don't live well in us. So you have a higher chance of getting an infection from a pathogen being in the water of the gear. This pathogen can come from anywhere but usually from the air you breath out onto the vial you are using.
I'm 53 and I think the best thing for you to do is testosterone. If you already have the winny go ahead and use it but test is your friend. A little side note about test prop. Many, and I mean many, people react baddly to test prop. Crippling pain and swelling!! It's better to use a long ester test or a combination of esters, such as sustanon.
The water based test is test suspension with no ester at all. It can be painful and it only lasts less then a day in your body. SO you need to shoot it daily. A long ester or a combination of esters can be shot once or twice a week. The only way to tell if you will react to test prop is to do some, and then it's too late of course.
My recomendation is to get some sustanon, or something similar, and do 250mg twice a week for a total of 500 mg per week. Add the winny by mouth at 50mg every other day or daily, up to you. Eat right, train multi joint exercises and kick your ass in the gym and you will enjoy the results. Don't eat right or train hard and doing gear is a waste of time and money.